The dangerous part of marathon recovery is not the first week, when everything hurts and nobody is tempted to train. It is week two, when you feel fine and your body is still repairing.
What the different markers say
Soreness: worst at 24 to 72 hours, largely gone within five to seven days. The least informative of the markers and the one everyone uses.
Muscle damage markers: creatine kinase and related markers of muscle breakdown can remain elevated well beyond the point the soreness has resolved. Structural repair is still under way while you feel normal.
Immune function: suppressed for several days afterwards, which is why post-marathon colds are a cliché with a real basis.
Resting heart rate and HRV: typically disturbed for one to two weeks. This is the marker most worth watching because you can actually see it every morning.
Running economy and performance: the slowest to come back, often three to four weeks before hard sessions feel right again.
The reverse taper
The most useful framework: run your taper backwards. You spent two to three weeks reducing volume before the race, so spend two to three weeks rebuilding it afterwards, and add intensity only once volume is back.
Days 1 to 3: walking, and nothing else you would call training. Eat properly and sleep, both of which do more here than anything else available.
Days 4 to 7: easy movement. Swimming and cycling if you want to move without impact.
Week 2: easy running returns, short and genuinely easy. No structured sessions, whatever your legs claim.
Week 3: volume approaching normal, still no hard work.
Week 4 onward: reintroduce intensity, starting well below where you left off.
Using your own data instead of guessing
The advantage of wearing something overnight is that this becomes measurable rather than a matter of opinion. Resting heart rate returning to your pre-race baseline and HRV rebounding are far better signals than how the stairs feel.
The pattern to watch is the one in the signs of overtraining: a resting heart rate that stays elevated and an HRV that will not rebound after easy days means the repair is still running, regardless of how good you feel.
On the shape of the taper before the race, see The Shape of the Taper.