Minimum time to get average structures

GROMACS version: 2018.8
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I have done a MD simulation for 200 ns and now I want average structure files for comparison and analysis. Is there any minimum timescale (interval) at which we have to extract those so as to get averaged structure ?
For example, in one reference, I found the average structures calculated using ensembles generated between 1 and 3 ns, for a total 3ns simulation run and there the ensembles were computed every 2 ps.