it is quantity vs quality imo
Please add some quantity or quality to your review count.
But what if one gets off on the idea of getting the girl off...
I don't actually care about them getting off however I do quite like RO and particularly 69, as such most WGs I've seen for 30 mins have pretended that I have got them off, primarily because I do quite a bit of 69'ing. I'm sure a few (nowhere near most though) weren't even faking either (due to various signs) but either way, personally I think 30 mins would be enough for you to "get most girls off", unless of course you need lots of shagging time (or perhaps in your case oral only) in order to cum.
In case anyone is wondering, I don't often mention 69 in my reviews unless they refuse. This is because I do start with just OWO (no RO or 69), almost all girls offer RO/69, no one's interested in whether I think they came and neglecting to mention 69'ing helps protect my identity.