Estimate session length for tabletop games.
Box runtimes rarely match reality because turn time multiplies by players and rounds simultaneously. Adding a player does not just add their turns, it also slows everyone slightly through more board state to read — modelled here as five percent extra per player beyond two. The waiting figure is the one that decides whether a group enjoys the game: at four players, three quarters of the playing time is spent watching.
Playing time
Play minutes = players x minutes per turn x rounds x (1 + 0.05 x (players - 2))
Downtime
Waiting per player = play minutes - that player's own turn time
Publishers usually quote experienced players at the lower player count with no teaching time. Adding a rules explanation and a new player routinely doubles a first session.
Simultaneous action selection, turn timers and choosing games with short interlocking turns all help. Otherwise reducing the player count is the most reliable fix.