We won't hold that against you too much
Is the time of the year going to make quite a big difference??
Don't get there much later than March.
Does having 500 hours make a significant difference to employment chances as opposed to a 200/250 hr fresh cpl?
Any experience is better than none. There is also a thing as too much experience. 700 hours may have you out of the running for Leos, but well placed for BAS or BAV.
MEIR will have lapsed...will this make a big difference?
If you're expecting a multi engine job then yes. If not, then no.
Does it help to chat with them and see if there's a possibility that they'll give me a call if something comes up later in the year? Does this even happen??
No chance, especially when there are guys still there from last season. Get to town, find a non aviation job or find a tree to climb like the rest of the green pilots waiting for a chance at a start and wait it out.