Our route planner can not determine the required number of rounds automatically. The max round time in the options will only help to divide stops over rounds, but it will not increase/decrease the number of rounds. You must set the number of rounds in the options manually.
The procedure to follow would be to set the max round time and an initial number of rounds in the options, find the route, check if each round is within the maximum duration and adjust the number of rounds accordingly. Repeat until the route meets your needs.