BASH - backup retain

I need some help with this - i have a backup retain and organize script I have a folder full of backups with the pattern like ReportsBackup-20140309-12-00. there is what I need:

1. remove all the files and just let the ones from 04-00h i have done like this

removals =`/bin/ls | grep -v -04-00`

rm /mnt/backupstorage/$removals

the question is how can I isolate the files base in the pattern ReportsBackup-20140309-12-00.per year and month ?

thank you