The documentation for the resource-usage call makes me think only the current usage is returned. Looking at the output seems to confirm that as there is no timestamp field in the data. I think the expectation is you will create a scheduled search that invokes resource-usage at intervals and saves the results in a summary index for later report generation.
There is another way. Try this search to get historical memory use (as a percentage).
index=_introspection component=PerProcess | rename data.process as process, data.pct_memory as mem_used | `dmc_classify_processes` | timechart max(mem_used) by process
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