Duration and Elapsed Time

Elapsed time is the duration between two moments. Grade 5 formalizes this calculation for complex cases: elapsed time that crosses hours and AM/PM boundaries, and elapsed time measured in hours and minutes simultaneously. Natural cycles (tides, moon phases, seasons, salmon migrations) provide real-world elapsed time contexts that connect mathematics to ecological knowledge. The tidal cycle of approximately 12.5 hours (two high tides and two low tides per day) is a natural elapsed time problem with both practical and cultural significance.