Ok, found a couple of insights here.
1.
https://fernworks.net/~dyeomans/Down...l.asp%3FId=510 (player commentary that it works in Plane of Sky at 6 p.m - this may be Sky specific, though)
2.
https://web.archive.org/web/20010418...ell.asp?Id=503
Web archive from casters realm specifying that the spell works between 8 p.m and 5 a.m. So, there's conflicting information. Source 2 seems, maybe, more reliable. But idk, that's for you to judge.