Methods to determine lifetimes of intermediate excited electronic states from up-conversion-luminescence transients induced by square-wave excitation pulses are presented. The methods are based on an excited-state absorption mechanism promoting population from a long-lived electronic state in the infrared to a short-lived emitting state in the visible. The methods are introduced for a three-level model system and applied to measure intermediate excited state lifetimes in three experimental examples of rare-earth or transition-metal ion doped insulating materials, namely CsCdBr3:Ho3+ Cs2ZrBr6:Os4+, and Cs2ZrCl6:Os4+.