The baseline windows are 1 hour for twigs, 3 for wood, 5 for stone, 8 for sheet metal, and 12 for armored building blocks. Current health scales the remaining estimate.
Start from current health
A damaged block has less of its decay window left. Enter the health percentage you can see.
Treat the timer as an estimate
Server settings and protection state can change the real result. Use the calculator for standard-rate planning.
Check each grade
Mixed bases do not disappear together. Lower grades finish first, which can open a route before the stronger shell is gone.