Based on one mile

2 min is 30mph, blistering and I doubt few of us on the forum are capable of it except down hill, or with a huge tail wind, myself included. It would take under an hour at this pace on flat to gently rolling terrain.

3 min is 20mph a strong pace and hard to maintain if you haven't worked at it. But under the same conditions above it should take an hour and 15 min.

4 min is 15mph which is a nice easy pace to ride 25 miles at depending on level of ability and/or climbing factors. It should take around an hour and 40 min at this pace. Still respectable and won't burn yourself out.

6 min is 10mph. Which means it is a ride mostly up hill, it is extremely casual, or a very new cyclist. 2 and a half hours.

And between these are all the other paces. Remember ride at the pace that is comfortable for you. No reason to really push yourself for it unless you want to get a high average or a PR.