It kind of all depends on how thick you apply the paint....... In most cases once the paint is dry enough to touch is when I like to pull the tape. If you wait too long, it is a good idea to run a (very sharp) blade along the tape edge. Just use enough pressure to score the paint edge. Otherwise you can risk damaging the job. Be careful when pulling tape. Don't yank it but use a consistant pace. I like to pull the tape at a 45ish degree angle. If you lay the paint on real thick, you may still have to score the paint edge with a blade. You are doing an engine not a show quality hood. Small errors won't be noticable on an engine block. JUst take it easy and use common sense and you will do fine.