I would heat treat it earlier, cause if you wait till the last couple days, it's a guarantee you're going to ruin it.

If you do it earlier, at least you'll have time to get more from someone else if you do.
That is exactly what I do. Each kid has one bottle of colostrum with their ID# on it. They get that until it's gone, which is the first day. I warm the colostrum in hot water in the sink rather than microwaving it too. Dunno if it really matters, but it makes me feel better, lol. Milk gets nuked on occasion.
I always try to breed the old girls to kid first. They have the best "stuff"! MaryAnne literally milks out gallons of colostrum, so I go out several days before she is due and milk some out of her so I can get a head start.
That didn't work so well last year, when as soon as I was done milking her, she went into labor! LOL. So then I had kids to deal with and STILL had to heat treat!
Last year in the kidding frenzy -- I had something like 5 does kid in one day -- I ran out of ready colostrum. So, at 11 pm at night, there I was at the stove. Got distracted at a critical moment and made pudding

So what to do? I dumped it in the blender, added a bit of store milk, and we were in business. LOL. Not a one of those kids had any bad reaction, and all grew up just fine!
Tracy