applications - Where can I find out when I installed an app?

Is there a Play Store log file?

Or should I be looking where apps are installed on the phone for time/date stamps?

Answer

TitaniumBackup also displays this when you go to the batch (backup/restore) tab. You can have it sort your apps by date of installation, name, size and so on.

It should be noted that you need to root your phone to do so.