How long should I estimate to get from landing at CDG (7;45am arrival), going through customs, getting to the RER B train, traveling to Gare du Nord and getting on the Eurostar train to London? I don't want to buy Eurostar tickets and then miss the train because it has taken me longer than I thought to get to it! thanks!
Passport check: 25 minutes
Baggage collection: 45 minutes
Walk to train station: 20 minutes
Purchase tickets: 5 minutes
RER B train CDG to Paris to Gare du Nord: 50 minutes
So about 2.5 hours to complete on average, no customs/baggage hiccups, no line-up issues, no mistakes and no train delay issues.
You might want to add on 30-60 extra minutes if you've never done this before and reduce stress.