how long it should take me to complete 3-10?
Everybody takes a different amount of time. The fastest people in 2021 finished Day 10 in under 10 minutes.
Personally, I just finished 2021 this past week. I was stuck on Day 23 for a long while... I was the 13945th person to get two stars on that problem. Apparently, three more people have finished the problem this week after me, so I'm no longer last.
As of right now, 219880 people got two stars for day 1 of 2021, and 61157 got two stars for day 10. If you're a pessimist, that means someone who gets two stars on day 1 has a 72-percent chance of quitting before day 10. If you're an optimist, it means 28-percent of the people who complete day 1 go on to finish day 10.
You can see the stats for all the days here: