On most yes you have to but you can use clothes peg's to hold the belt onto the other pulleys and use lipstick to mark where the cam and belt tooth line's up.
I would still re-check timing as things move but you have a huge head start. God Luck
Just put the engine at TDC firing on number one, with some twink mark a like across the belt and pulley tooth on both pulleys then whip the belt off, to put it back on just line up the white twink marks, then Bob's your uncle.