Space

whether a time limit is placed on a specific siege warclaim depends on the leaders negotiating terms, for instance the last siege in the oren-dwarf war on bloodnight's fort had a clause stating that all the attackers had to be killed for a defender victory, no time limit.

i'm guessing leaders have the option to have a time limit so people aren't sitting around doing nothing for 3+ hours bored out of their minds while the battle happens