Effort is a subjective thing, while time obviously depends on how fast you go! In the last three years I've done different endurance events. I've swum from Alcatraz, run half-marathons, cycled century bike rides, and done Olympic triathlons. From this data, I have come up with approximate transforms of distance to time and effort.

Time is relatively straightforward. The following are baseline speeds that are roughly equivalent for me:

2 minutes per 100 yards

18 miles per hour

7 minutes per mile

To gauge effort, I took my estimated times for each event, and multiplied them by an 'effort scalar', based on how much effort I find each activity relative to the other. These values are entirely subjective to me, but reflect my experience: cycling (even at 18mph) for an hour is significantly easier than both swimming and running for an hour; running for an hour is marginally harder work than swimming for an hour.

1.8 × bike effort

1.0 × bike effort

2.0 × bike effort