How long after the race was called did Obama resign his senate seat?

This only means anything if it breaks a pattern. If it's normal not to resign until after electoral college votes, it means nothing.

Edit: I checked, Obama announced his resignation on the 13th, election was on the 4th. So same amount of time has passed as of today. If Harris goes much longer without resigning, it's suspicious.

How long after the race was called did Obama resign his senate seat?

This only means anything if it breaks a pattern. If it's normal not to resign until after electoral college votes, it means nothing.