When should you ask for a second date?

Im having the first date of my life tomorrow with a girl and we have been texting at least a bit everyday for 20 days and we both have even discussed things we could do in future dates , so it seems she is interested in having them before even having the first one

My question is, if it goes well, should I ask her at the end of the first date, when I arrive home or a few days after?

As I have time next weekend but will be busy the rest of the month, I was planning on saying at the end of the date something like "I had a lot of fun with you and would like to see you again if you want to too" . Or should I wait a bit ?