Rounds per level, minutes per level, hours per level… or some random number of rounds, minutes, or hours, or a combination…
This gets to be a pain to manage. I can’t be bothered to count things too carefully, especially when most of the time the duration doesn’t run out while it matters.
Instead, durations last until certain conditions are met, or are no longer met.
I have found that once you are past a certain level (about fifth), in practice “rounds per level” basically amounts to “until the fight is over” (things intended for use outside combat typically don’t have durations measured in rounds). I think I’ll replace durations measured in rounds with “until you stop fighting”.
Similarly, durations measured in hours often amount to “all day”. I’m going to go with that — I’m replacing durations measured in hours with “until you sleep”. Or “until sundown” or “until sun up”.
Durations measured in minutes looks like it should be more difficult to quantify this way, but I have typically seen it mean “go go go until we can’t”. Effects with durations measured in minutes are often buffs and the like, so PCs like to push as fast as they can while the buffs last. Durations measured in minutes will now last until a “rest” is taken.
A “rest” is a specific mechanic in Echelon, taken from Trailblazer. You can read the Trailblazer Rest Mechanic as presented originally at KJD-IMC. The short form here is that formally taking a rest allows you to recover various resources (notably hit points — the Hard to Kill hit points, not the actual physical trauma hit points, as described in On Hit Points and Healing)… but ends medium-duration effects. In this case, anything with durations previously measured in rounds or minutes would end.
This aligns pretty closely to how I’ve actually seen it play (with the exception of the hit points recovering — though with a healing stick, a wand of cure light wounds, it’s not far off).
If you want to regain the former complexity, simple go back to the rounds/minutes/hours per level calculation. I find it doesn’t add anything I care to have, but it does make character level a little more important in calculation.