Definitely reduce your press time - if not, you will burn the koozie - I know from experience

I only press about 5-10 secs - but it took me several trials to figure that out! I do the same on mouse pads and coasters - anything of that material. I just used one koozie and tested several areas with strips of transfer until I got it right.
I also remove the lint before pressing. On a few koozies, I noticed lint under the pressed transfer - it took me a while to figure out what it was since the lint was not noticeable before the transfer was put on. I didn't have a lint roller at the shop, so I took a scrap piece of vinyl and just used the sticky side to remove the lint - worked very well.
Good Luck!