Hey @Bill 

Last 30 days will allow you to capture users in this cohort who have had the Version property = 5.372 anytime during the last 30 days vs the last 1 day.

So if user A had the Version property = 5.372 on June 15th and Version property = 6.372 yesterday , they will be included in the cohort defined using “last 30 days” ( let’s say cohort A ) and not the one using “last 1 day” ( let’s say cohort B ) . If they had the same Version property value for the last 30 days, then they would be included in both the cohort definitions i.e. cohort A and B.

If you had selected the most recently clause, the property value will be drawn from a user's most recent active event. 

Let me know if I have interpreted your use case correctly.