The race record is the most likely to be broken, realistically only by Hamilton.
With respect to Hamilton, his longest interval of time taken to win 20 races spans 2008 to the beginning of 2014; 7 years of race entries - even though this was achieved early in 2014. Bear in mind that during his entire McLaren career, 6 years, he "only" won 21 races.
Since joining Mercedes, his average time to achieve 20 race wins has averaged 3 years, if you include the 2013 year; 2 since then.
Schumacher himself took 3 years (2004-2006), including the mega-dominant 2004 where he won 13 of 18 races, to move from 70 wins to 91.
Considering the increased competitiveness of Ferrari (hopefully Red Bull), my vague forecast would be for late to mid-2021. Any major shift in competitiveness pushes this out by years though.
The best case scenario is, 2 more years like the last 5, end of 2020 he has 7 championships and 90-92 race wins.