By default, BranchCache data will remain in the client cache for 28 days - if left untouched.
If the data in the cache is accessed for instance to provide content to another BranchCache Peer requesting that segment of data, then the counter is reset to zero.
You can set the cache expiry time to suit your needs using the following powershell cmdlet (click on link for cmdlet info)
For example, the following specifies that content information and content remain in the cache for 100 days. After 100 days, untouched in the cache, the content will be deleted.
PS C:\> Set-BCDataCacheEntryMaxAge -TimeDays 100
Please note that this only applies to content placed in the cache AFTER this cmdlet has been run.