Yes, you can start your pool at any time after Week 1.
For NFL Pick 'Em Pools:
Go to your Commissioner Console
Click Pool Settings
Navigate to Pick Settings
Under Pool Starting Week, select the desired starting week
For NFL Survivor Pools:
Go to your Commissioner Console
Click Pool Settings
Go to Pick and Scoring Settings
Adjust the Pool Starting Week accordingly
Want to add a twist to your Survivor Pool? Check out tie-breaker ideas here.