They apparently didn't touch the silver/gold times for the X1. Just judging by what the times are now for bronze, as long as you finish it should be pretty easy to bronze them all. When I bronzed it (with the older times), it took me about an hour on Monza, another hour for Suzuka, and about 3 hours for Nurburgring GP (this is definitely the hardest of the three, in my opinion). After doing the Suzuka 1000km in the X1, I still wasn't even close to the silver time on that course.
Also a tip for the X1, you lose downforce at an exponential rate when you brake. A lot of corners that you would normally have to brake pretty heavily on in a normal car, you just need to slightly take your foot off the gas. The last chicane of Monza, the two turns after the esses in Suzuka, and quite a bunch of turns at Nurburbring all need to be taken at just about full speed.
XI Wiki


