It depends on the algorithm. The maximum delay is around 1 second, but if there is any pitch shifting or modulation the maximum time will be shorter. The minimum time can vary as well, and you'll have to take that into consideration.
The delay time pot is a voltage divider so if you set the digipot to 50% of its value the delay time will be approximately half way between whatever the minimum and maximum times are. Changing either extreme will affect the ratio.
Do you already have an FV-1 project in mind that you plan to add this to? There are going to be some new digital effects added soon that will have integrated tap tempo with no workarounds needed.