I think the studying was worse. I was constantly double guessing myself. "Did I do enough compressible fluid flow problems? Nah, I don't need to worry about that. I'm HVAC. Well, maybe I should brush up on it. No, I need to focus on heat transfer problems". That was my brain during the two weeks leading up to the test.
Did you ever figure out how many hours you spent studying? I know I was probably around 125, but then I only started 6 or 7 weeks before the test. I hope it was enough.
Also, I started studying in November because 1) I'm just that kind of over-prepared person and 2) I knew I'd have travel, holidays, toddlerness, and evening work meetings interfering with my study schedule.