Whe I hotfix stones, I wait about 6 hours, then, go around carefully with a pin or needle and check for adhesion. If it's not "stuck" I reheat and restick it. I ran into a batch of stones recently that had some issues with the glue (first time ever, and yes, real Swarovskis) - and resorted to using a small amount of glue to hold them down where they didn't stick. Usually, I might get 1 out of 300 that doesn't go down firmly first try.
A few bejeweller things ... I have a range of tips in all the sizes. I generally use the one size smaller when I attach them; I find I have less chance of them getting stuck in the tip and having to lever them out with a pin. I also use the hotfix "spot" tip quite a bit, I've found that by holding that one on the top of the stone and then moving it around the edges I get great results. This works really well with the small ones when I've done a close placement for effect.
I also will put the dress on the ironing board with a pressing cloth and heat them up afterwards. I have been using SS34s lately, and I am absolutely neurotic about losing them.
I know it sounds like a lot of work, but, I don't like using glue (just can't get the hang of it). I had to do glue recently due to a need for a shaped rhinestone and some ss40s, and I cursed those things left right and centre; I do really fine embroidery and the like, but, can never seem to get the glue perfectly covered no matter how hard I try, and it seems to take forever! I think it took me about 30% longer to glue ... I know lots of you find it easy and are way better than I, I'm just glue-hopeless.
To take them off ... you can reheat and then carefully lift them off. Test first. Some materials will show a mark where the glue used to be, some it works beautifully.