Players may say their adventurers in a dungeon “spend a round searching the room,” but RAW such an action takes much longer than one round. Under the D&D 5E rules, if searching one square (5 foot by 5 foot) takes one action in a round…
Size Of Area … Time To Search
* 5′ x 5′ … 1 round (6 seconds)
* 10′ x 10′ … 4 rounds (24 seconds)
* 15′ x 15′ … 9 rounds (almost one minute)
* 20′ x 20′ … 16 rounds (about 1.5 minutes)
* 25′ x 25′ … about 2.5 minutes
* 30′ x 30′ … about 3.5 minutes
* 35′ x 35′ … about 5 minutes
* 40′ x 40′ … about 6.5 minutes
* 45′ x 45′ … about 8 minutes
* 50′ x 50′ … about 10 minutes
* 55′ x 55′ … about 12 minutes
* 60′ x 60′ … about 14.5 minutes
* 65′ x 65′ … about 17 minutes
* 70′ x 70′ … about 19.5 minutes
* 75′ x 75′ … about 22.5 minutes
* 80′ x 80′ … about 25.5 minutes
* 85′ x 85′ … about 29 minutes
* 90′ x 90′ … about 32.5 minutes
* 95′ x 95′ … about 36 minutes
* 100′ x 100′ … about 40 minutes
Just searching walls for secret doors should take much less time (1/3 duration noted below, but at least one round). Advantage should be given if taking extra time or if adept at the surfaces involved (like dwarves’ stonecunning underground); disadvantage should be suffered if rushed, searching a cluttered room, or searching while distracted (being shot at every round, searching a room on fire).