How much time should you wait before having sex with your partner?

There is no magical time of reference for you to wait to have sex with your partner. When you are both ready and willing, physically and emotionally, things will happen naturally. If you try to force it, one of you will speak up and if that happens then respect that persons wishes and wait. Let it flow my dudes. Chakra and all that jizz. I mean jazz.

Normally it would take me about a month of dating at least, but last night I had the first date with this girl and we almost had sex. I hadn't expected it, so didn't have any protection with me... I probably still wouldn't have, because I actually need a bit of time

There shouldn't be a time. Every couple/pairing is different so you could hit it off the first night and get to physical play (helps if you're in the right environment where that's what people are interested in, like a bar/lounge with a dance floor). If you're going through the relationship route it's going to take longer just cause that's how courting is in society...it's a lot shorter than it used to be! I don't think physicality should be purposefully withheld. I think though there still needs to be safety in all areas (some more than others), we still need be realistic and voice your opinions. There's going to be a few compromises but people are different and if it's something she or you want while the other doesn't...be honest and bring it up tastefully (like the day after you had a hot night) and talk about real expectations on both sides so you don't become bitter/frustrated/overwhelmed later. You'd both be much happier leaving a relationship early if later sex expectations leave things awkward.

I'd wait until either they wanted to, or until I felt like we were both comfortable in the relationship at that point where it may seem like an option.