In my games we go with these assumptions on the medicine skill checks.
Reducing Bleeds: This covers things like Sutures, Application of Styptic and bandages.
This is instantaneous and happens when you make a successful Skill check.
Resuscitation: This covers CPR, de-fibrillation or the use of adrenaline to bring someone back before they’ve “crossed over”
This is also instantaneous and happens when you make a successful Skill Check.
Regeneration Rate Increase: This covers the bonus to healing you get when “following doctors orders” as in Bed rest, taking it easy or walking with a crutch.
The rate increase occurs when you make the check but usually it goes away when you do anything strenuous. Depending on how severely your injured that could mean a lot of things. In cases of extreme injury I rule that you lose the bonus as soon as you get out of bed until someone makes a new check, in the case of minor injuries it sticks around until you do some wind sprints or punch someone in the junk.
Hopefully that helps. I think the time was left vague specifically so we could come up with the reasons above. If they have stated flat out that the regeneration lasts for so many cycles it would be easier to find some way to abuse it then force the abuse on the GM by using RAW arguments.