I would wait 1 week to identify the top performer. You can change the amount of time to see what works best for you.
There will always be periods of profits and periods of losses. There are many strategies that can be used to minimize losses so that over the long term the account will be profitable. One strategy is to have several Expert Advisors trading. When one EA is going through a period of drawdown the other EAs may be going through periods of profits. Another strategy is to have a demo account of the 7 EAs and only move the Top performer to a live account or maybe the top 3 performers. Then once each week (you can change this time to see what works best for you) review the demo account and move the top performers to the live account.
Hope this helps!
Alan,