i think it partially depends on how long you were alive, if you died super quick after a respawn it will be closer to 20 sec, if you stayed alive for like several minutes then it will be shorter
i have my main house (grand topal hideaway) listed in the housing tours, it has multiple target dummies, scribing altar, and grandmaster stations (in progress being filled out), as well as almost every antiquity furnishing on display to preview them
BGs have a global cooldown of 20 seconds for ressurrection. After the cooldown ends, the option for ressurection will be available. So, if you die close to the global cooldown end, you'll have to wait less than if you have died at the beggining of this cooldown.
Also, this is a global cooldown that works for all players, that's why several times you ressurrect at the same time as other teamates (enemies will also ressurrect at the same time as you, but it is really hard to notice, because bases are far apart from each other).