I expect 3 hours out of a cloth nappy , any less then i wouldnt use it as cant be faffing about changing a 21 month old busy toddler every 2 hours - he'd go nuts!
Normal change routine for us is:
7am - out of night nappy into fresh nappy , normally a BBSS no extra boosting as he poo's at about 10am!
10am ish - change dirty nappy put a nice show off nappy on for the morning (even thiugh theres no one to show off to but me!)
1pm - change into a fitted & wrap for sleep as pockets cannot cope with his naptime
4-5pm (normally another poo around this time) change into another showoff nappy for the afternoon
6.30pm change into night nappy