I have been thinking how much time you should spend with a girl before number closing her?

I am under the impression from reading different material, that I should number close after talking for 10-20 mins at the high point of the conversation, but it just doesnt seem enough.

For example, I managed to open a girl buying drinks for friends at a bar. There were good rapport, a lot of kino and she almost forgot about buying drinks for her friends. I know she will have to go back to her friends very soon, so I decided to number close, after I made her laugh really hard. I then said "It is really interesting talking to you, but I need to go back to my friends. How about we talk some other time?" She said yes but didnt ask for my number directly and I had to give her a little nudge there. It was all in all very smooth. Then I said "we are going to a different party later on. I will text you. Maybe you want to join", which I did, but got no reply.

The next morning, I thought to myself, I only spoke to her for like 10 mins, and I cant even remember how she looked like! She must feel the same. I did try to ask her out two days later, got a reply but it doesnt seem promising.

How much time do you guys spend before number close? What should be the ideal amount of time?

You goal should be sex, not the phone number. The phone number should be the backup plan if logistics mean you can't go for the same night lay. I don't want to give my number to every girl I lay, it can get messy.

Learn how to escalate towards sex. There is no right answer to your question. If a set is going well, why eject and create a barrier between you?? Ejecting from a set should be done when the interest level is low, normally early on in the night. Get the number and set up day 2's, nothing wrong with that. By the time it's midnight, you should be going for make-outs and SNLs, not phone numbers. Once you get her number, you give her all the power. SHE chooses whether to answer your calls, SHE chooses whether to reply to texts and even if she does reply, it's on her terms.

I generally only give out my number if the girl asks me for it, seems very into me and is submissive in her behaviour.

That is a very interesting point of view. Any good material you would recommend for sex escalation?

I dont want to be seen needy, so I always tend to take the slower approach by number close. I think you are totally right. It depends on what level of interest she is showing. In my example, she was clearly showing good interest and it was silly to cut it off. On the other hand, I thought if I cut it off while at high point then she would want more.

On the side note, if I stayed for longer, she will inevitably need to go back to her friends after she bought the drink. I was not sure what is waiting for me there. I will need to open the set even though a connection has been establish with the girl and there is always the risk of a fuck up there. So I thought the least risky way was to take the number and call her later. Have you ever come across situation like this, where the girl was isolated first naturally but have to go back to her set very soon?