A few years back I made this same statement, that if I didn't know after three weeks if a woman was someone I could marry then I was asking the wrong questions. I can see where this would seem foolish but after meeting the woman that became my wife online, I asked her to marry me after 18 days and without meeting in person. We have been married over five years now and I married a gem that I appreciate to the hilt.There used to be a blog (now defunct) called "The No Nonsense Man" by Marc Rudov (correct spelling?) There were a number of useful relationship articles, including one that examined the vast amount of unnecessary time couples waste by dating with the usual & prolonged 'getting to know someone' approach. This still stands out in my mind:
"Three weeks" is all that it takes, if the couple have a mature attitude, to determine if they are respective marriage material.
So your 10 weekends (20 days) is sufficient. Make the time together count, and be upfront with each other about where you both want the relationship to go, and why.
Regarding the online aspect, Max Roscoe is correct about actually having to truly 'get to know each other', since your dates can't revolve around the typical external (distracting) stimuli.
I believe that many marriages fail due to the couple not laying a solid foundation while dating; most of their 'together time' being focused on "having fun"/being compatible because they share the same taste in [insert recreation]/showing each other off to their friends/etc.
There is no magic number of days of course but since that time I have read stories of people who got married in a lot less time that we did (< 8 weeks) and were together for decades. I hope that some men can find some hope in that because while it can take a loooong time to meet someone, it can also take a short time if you are both on the same page. I don't claim to have known every thing about her but didn't want to and that can just drag things out. I got the information I needed, basically she was a Christian, and that was that.