Yes the top was tricky but snapped it on. I thought if I bumped up the temp it would restart the whole countdown on days left? I guess that won’t matter since it’s marked on calendar though.You could bump the incubator up to 100 degree setting, to see if it's then able to maintain 99.5 degrees. There might also be a draft or the cover might not be "perfectly" attached. I've had quite a bit of trouble getting the top to connect exactly.