What is the maximum volume one should do for a tempo session, if they can only do it once a week?
If you’re limited to only one tempo session per week on the track or pitch I would still keep the volume the same (i.e. 2000m) and try to supplement it with another type of low intensity workout on another day or two (e.g., indoor tempo, bike tempo, pool work, etc.). Spread the work out using different methods on different days rather than trying to get in a full week’s worth of tempo in one running session.
I’ve done 2x3000m and it worked for me.