ERA5-Land accumulations are calculated differently from ERA5

"The accumulations in the short forecasts of ERA5-Land (with hourly steps from 01 to 24) are treated the same as those in ERA-Interim or ERA-Interim/Land, i.e., they are accumulated from the beginning of the forecast to the end of the forecast step. For example, runoff at day=D, step=12 will provide runoff accumulated from day=D, time=0 to day=D, time=12. The maximum accumulation is over 24 hours, i.e., from day=D, time=0 to day=D+1,time=0 (step=24)." - see ERA5-Land: data documentation#accumulationsAccumulations for details.

Relevant useful links:

ERA5 terminology: analysis and forecast; time and steps; instantaneous and accumulated and mean rates and min/max parameters

ERA-Interim: 'time' and 'steps', and instantaneous, accumulated and min/max parameters