Plans tend to be written for the week you would like to have: an hour, four days, no surprises. Then a Wednesday arrives with one meeting too many, and the choice becomes an hour or nothing. Most people pick nothing, twice, and by the following week the plan is gone.
A smallest-useful version solves this. It is not a consolation prize; it is the session that keeps the thread intact.
What a 15-minute version looks like
Pick two movements that cover most of the body — a squat or hinge pattern and a push or pull — and do a few sets of each after a brief warm-up. Add a short walk if there is time. That is a complete session for the purposes of staying in training.
The rule is that it has to be easy enough to start on your least motivated day. If it requires a decision about programming, it is too complicated.
Why it works
A reduced session does very little for fitness on its own. What it protects is frequency, and frequency is what most plans actually lose first. Two short weeks beat one perfect week followed by three off, both for strength and for the simple fact of still knowing where your shoes are.
It also removes the all-or-nothing arithmetic that turns one missed day into a missed month.
What not to do
Do not cram an hour of work into 15 minutes by cutting all rest and racing to failure. That produces a miserable session and a sore next day, which makes the following short session less likely. Keep the intensity moderate and finish with something left.
And do not make up the missed volume at the weekend. The activity level in a TDEE estimate describes an ordinary week, not a debt ledger.
The long view
A realistic plan has three sizes: the full session, the short session, and the walk. Most weeks use all three. None of them needs to be impressive for the year to add up.