That seems about right, though as you imply, history tells us that Spielberg isn't likely to need six months. Since the release date has been pushed back a year, it is reasonable to think that's how long the shoot is to be delayed as well. The original plan was April 2019, so Spring 2020 seems proper. WEST SIDE STORY is shooting at the end of next summer, and Spielberg does tend to make movies in pairs when returning from a hiatus. And anyway, it is really the last chance.
A lot of things have to go right for them to get that chance, too. They have to actually come up with a script after ten full years of reliably failing to do so, Spielberg cannot decide for the umpteenth time to find something that excites him more, and several members of the team have to stay healthy at an age that people die of natural causes at. Ford is the most important player, yes, but we certainly want folks like John Williams and Michael Kahn to be part of the finale.
On a more optimistic note: Scorsese finally got THE IRISHMAN through production despite lots of reckless delays, so we have a precedent of something like this actually happening despite all odds.