They will be illuminated for up to 2 hours after sunset and before dawn. That’s all night at these latitudes at this time of year. Over on Twitter there is a great deal of discussion which includes amateur and professional astronomers.
https://twitter.com/doug_ellison/status/1132443682018226176 is a good place to start.
One person points out that when in a few years time the whole 12,000 constellation is in orbit, SST will be on stream and observing much of the sky every night. Even if spread out as far as possible there will be one Starlink satellite every 3.4 square degrees. The field of view of LSST is 9.3 square degrees. (Apologies for having 1.5 in the first version of this post).
It’s going to be a nightmare.