Although an apartment we were looking at back in December seemed not very well-kept (among other things there was cat/dog food laying on the floor and bugs flying in the kitchen) - we were assured it would be thoroughly cleaned, so after discussing a few things we then signed a contract in January to rent it starting April 1st.

The then tenant was leaving end of February and we were told we could technically start moving in sometime in mid March if we agreed to pay the heating and some other costs, which made sense.

Fast forward to this week, we've had a quick visit to the apartment to take some measurements and our new landlord and I verbally agreed to do a key/apt handover this coming Thursday (18/03) for us to start slowly moving in over the weekend. We then stayed there for about an hour taking measurements, hanging around and planning the future furniture arrangements.

When entering the apartment we took out our shoes and my wife's white socks soon have turned to being much darker, we also noticed that in some areas the floor was sticky and found some leftover dog/cat food and broken pieces of glass (!) behind the kitchen door.

When leaving - we mentioned to the landlord that the apartment wasn't as clean as we hoped for it to be, but he waved it off saying that it surely hasn't been renovated and there must be some dust there by now and we unfortunately ended up dismissing the topic and switching to something else (like doing the laundry was only allowed once in two weeks which was equally important and even more inconvenient to us).

The next day he sent us an email asking to confirm that we'll be paying 1/3 of Nebenkosten, Heizkosten and a full electricity bill for March (emphasizing that this is still great for us financially) which is indeed more or less what we agreed back in January, and seemed fair to me.

Paying for the electricity in full for entire March seemed a bit off to me so I asked about that. Given that he brought up our agreement from January - I also pointed out that the apartment wasn't as clean as we agreed for it to be back in winter, listing the above points (sticky floor, white socks turning dark, found pieces of broken glass & animal food, white walls in scratches and drawings), and said that given that there's not that much time to do much about it - we'll clean it ourselves and maybe mention it in the handover document.

A few hours later he is calling me in rage saying to forget about the agreement, there will be no key handover on Thursday, there will be no move-in over the weekend. He'll clean the apartment, it will probably take a lot of time so we can move in on April 1st now. If the apartment will be cleaned before then - he may consider allowing us in if we pay per day, prorated monthly rate.

I apologized for the email making him upset and stated that I only pointed out the facts and our agreement, but he kept repeating to forget about it and how ungrateful I am (and how some people just hate to hear the truth which I suppose was a self-reference), and that he has never offered such nice deal to anyone and so on and so forth, and that from now on he'll have two other parties present when talking to me.

After the call I sent him an email restating the same thing: apologizing for the email making him upset, saying that this was not my intention, and hoping that he'll keep up to our agreement and reconsider his decision and still do the key handover on Thursday, as agreed earlier.

Our verbal agreements were obviously not put in writings anywhere.

I now assume I won't hear back until the apartment is properly clean, which is good I suppose but will likely take a long time & goes against my planning:
- I took a day off of work on Friday to start packing
- I made a reservation for a moving truck on Saturday as well as made some arrangements for help
- I also informed the current landlord that I'm leaving a week earlier
- What makes things worst for me is that my wife is due in mid April, which technically could happen anytime before as well, and longer we wait - the higher the change is

I am not really sure how to proceed now. Assuming I won't hear from him - I am thinking to give him a call on Thursday morning and if he still refuses - try to get his son's contact (who is actually the owner of the building but lives in a different canton and I'm dealing with his father know who is acting on his behalf), in hopes to have a more sane conversation, but I doubt I'll get his information.

Are there any other options I could consider here?

Given the huge wall of text, here's a TLDR:

new landlord is in range I pointed out the apartment was not very cleaned (containing pieces of broken glass, dog food, etc) and now he won't let me move in on the agreed date (before the contract starts) despite all my arrangements (moving truck, day off, help arrangement, etc)

re-schedule the move date

life lesson: there's give and take, if you're not going to give, don't expect to take.

So you can(could) move in in March rent-free and you still want it spotless?

As far as I understood from OP's wall of text, the deal was that in exchange for moving in earlier than agreed in the contract, they had to pay the electricity for the entire month i.e. March, a third from Nebenkosten and heating. It wasn't exactly for free, considering the apartment was going to stay empty anyway.

He is in his right to refuse you entry till April 1st and unless there are witnesses to his agreeing you could move in early there is little you can do - apart from re-arrange the moving date.

From my experience, when we allow someone in early, as a favour, and the apartment is not yet fully cleaned,we make it clear that they take the apartment as is, and apart from damage, they will have to make the thorough clean themselves as well as being liable for heat, electricity etc. Tenants are usually grateful to be allowed in early so agree to the condition.

With hindsight, I guess you should have said nothing and just cleaned it yourself or had a congressional cleaner in. You'd have still been quids in.

Notwithstanding the above he seems a bit difficult and i hope the rental goes smoothly going forward.

My only suggestion would be to apologize again, and invite him to a restaurant for a lunch or dinner in order to heal the relationship, but saying you respect his decision. Over a few drinks he may mellow and if you offer to clean the place he may relent. At worse it will cost you the price of a meal!

Just another thought. If you suspect the landlord will be difficult, and it seems he is, I'd engage a professional company that will inspect the flat at the handover, without you being there. They will make a protocol of anything that is wrong / damaged /unclean, especially the appliances and carpets, for the landlord to remedy. They then hand the keys to you and you move in. Then use them again when you decide to move out.

If the landlord does not remedy them then you have a clear case to deposit the next rent at the conciliation office.

It will cost a bit but more than worth it for the peace of mind it will give you.

And once last thing, washing room access every two weeks is wrong. You are entitled to weekly access. With a baby you'll certainly need it!