slower is generally better.. but there is no proper research on this.. this something that requires large samples across varied physical properties of the buds -- density, for example. Lots of confident guesses based on anecdote, but no refined answers with evidence to support it.
slow.. if it takes 7+ days, you are generally doing it okay. I find i need about 9 days at 68F / 60% for most bud... density of the buds will impact this. I remove buds from stems, so it'd be a bit longer if i left them as you do on the stem.
64F is still quite cool, so that's not going to harm anything. Expect a 10+ day dry, which is excellent.
The most volatile molecules can 'boil' off (sublimate? better term?) at low to mid 70F, if i recall... but many have a BP up around 400f, too. It is a wide, wide range.. which matter? which do not? there is a whole shit ton of info we are assuming andn simply don't admit to the profound ignorance that exists on these subjects that need more study.