all the advice i've gotten is to ask them out within 3-5 messages, any less is too soon, any more and she will lose interest. while that might work for some, i think it's best to feel it out and talk to them first. i know i talk way too much and it seems to kill attraction.
I get the idea behind ask them sooner then later. Too long of a build-up kills interest for sure. Then again I was pretty confident that worst case scenario my dates would be at least a fun conversation for an evening and that's how all of them turned out. So I guess there's just a bit more risk of having less of a connection if you haven't talked as much. Then again I'm not too hot on who I've met so far so nothing to lose