If it's a scratch/scrape you can leave it for as long as you can stand seeing it
If it's a chip/crack then my advice, get it repaired/replaced as soon as possible, in the cold weather it's even more important if there's a possibility of ice as that can expand it and make things worse.
In Luxembourg like the UK it's covered for free by my insurance, and when I got my second impact not long after getting the STi it was a chip on the passenger side and repairable. Carglass (Autoglass in UK) repaired it and they also treated the older scrape to almost getting rid of it - very clever.
If the worst happens and they have to replace the screen due to it's location, but also should be covered, then make absolutely sure they get you an original Subaru screen. When they needed to replace the screen on my old WRX they tried two 3rd party screens before eventually getting an original, as they stood proud of the car at the roof and made a lot of wind noise.
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