On the evening of October 14 (JWST starts at 20:00 UT ), we'll have a coordinated campaign with all the telescopes above on V404 Cygni, which is a quiescent black hole X-ray binary. It's about 16.6 in R in quiescence, and it's relatively red due to foreground extinction. It would be great to have some folks in Europe get some additional photometry. Hipercam on the Gran Telescopio Canarias will already be observing, but it would be good to have a backup in case of bad weather (which seems likely given forecasts for La Palma).
In the past, flaring at the 10-30% level has been seen on timescales of ~hours, so if anyone can get good measurements with time resolution of about 15 minutes for some timespan starting a bit before the JWST data, and extending a bit after, that would be incredibly helpful to put the observations into the longer term context.
This article is in the public domain and shows some past examples: