I personally am not judgmental towards people and their sexual habits, but here are my two cents:
I think that the right time is when both sides are ready for it. For dudes who have unrealistic time limits (i.e. 3 dates), it doesn't mean you have swag, just you are too thirsty and aren't discerning. Most guys can wait out within reason for a girl they really dig. If you just want to get laid

but don't get mad if things go sideways.
Me personally, I actually would purposefully not jump into the sack for at least two months or so. Mainly because
1) I was more discerning about women and I only went after women with multiple attributes I liked - not just some girl with a big ass or nice face. It made the investment in time more worthwhile. I didn't feel like wasting time with dumb bish I knew I wouldn't care about after busting my nut
2) I detest materialistic/big spending/psycho/conceited chicks. I need to give myself 1-2 months to get past the initial fake dating stage where everyone puts up a front, looks nice, tries to sound intelligent etc. Eventually the mask slips and I can see if it is worth my time or if I should bail. Also, I can tell the type of chicks who are going to think they 'own' me or I owe them something if I get p*ssy. Whatever
3) I know too many guys who have gotten trapped with kids or STDs. I don't know why dudes go raw with someone they haven't even known a month. Even with protection though, I became extra cautious about the coochie I dove into
4) Sex does distort relationships. I have seem too many dudes get caught up (or even married) to chicks whose bomb p*ssy clouded their judgment on her other (usually negative) attributes. Trust me on this: a good woman is worth putting the effort in to improve sex, a bad woman isn't worth the effort no matter how good she rides it. Part of the whole 'good sex' problem anyway is people (men and women) don't communicate these days. The average girl, who you have a good relationship with, can learn the things you like and do it for you. Unless she has anatomic issues that make you a mismatch or isn't physically attractive, she can learn to do it right. Dudes want a girl that is the shyt in bed on the first lay and then say they don't want someone with a body count.

EDIT: yeah, larger sexually compatibility can be a deal breaker if you two just aren't compatible, but this is different than "good on the first lay"