Must I fill out the C3 twice?

I realise it's a long shot, but asking anyhow.

I'm flying over with the furballs tomorrow, landing Friday morning. The C5 and all their nonsense is sorted. Because I'm staying for just 55 hours, I hardly need clothes and am bringing over as many personal possessions (as the C3 calls them) as possible. My actual moving of my actual self isn't happening until 23 May/arriving 24 May. At which time I'll be sending the rest of my crap via a cargo service.

So, with that preface, three questions:

1. Do I need to fill out the C3 both times?

2. If so, what do I put as my moving date on the C3 tomorrow, 12/4 or 24/5?

3. Also if so, how (if at all) does it affect my filling out the C3 form the second time?

FWIW, my inclination is to fill it out both times (this first time as a precaution against potential customs issues), put my moving date as 24/5 each time, and answer the various items accordingly (e.g., "no" to the temporary visit question, because the 12/4 visit will have been temporary and not moving, even if I will activate my visa that day).

I welcome all feedback on this, and I'm aware that I'm doing everything backward and stupid, but with a demanding job, the last semester of a second degree and a novel on the go, I'm just trying to make things manageable/avoid a mental breakdown.

Hi seahorse!
I read your questions and had a look myself at HMRC but I really couldn't work out what one would be supposed to do in this situation.
I meant to suggest that you ask your shipping company but I got side tracked  and you'll be here by now anyway!
The cats made it OK?

Yeah, I ended up filling out the paperwork just in case, but I wasn't bringing anything naughty into the country (mostly cat toys, their favourite blankets that they've stolen from me, some cardigans and the 18L stock pot), so I just went through undeclared. I'll deal with the C3 when I come home for good.

The kittens arrived healthy and tired, and have adjusted nicely. A big weight and another stress off my shoulders. Thanks for asking!

Yeah, I ended up filling out the paperwork just in case, but I wasn't bringing anything naughty into the country (mostly cat toys, their favourite blankets that they've stolen from me, some cardigans and the 18L stock pot), so I just went through undeclared. I'll deal with the C3 when I come home for good.

The kittens arrived healthy and tired, and have adjusted nicely. A big weight and another stress off my shoulders. Thanks for asking!

So glad to hear that you all made it in one piece. What a relief to have that part over with!   
Good luck with the rest of the move!