I presume you are referring to the main Microsoft Dynamics\GP or Microsoft Dynamics\GP2010 folder itself that typically resides within C:\Program Files (x86)\...
The Date on this folder gets modified if you change the installation - such as Add/Remove Features on the GP Client. It also changes if you apply a service pack.
On GP2010 for example, a service pack creates a backup folder also: for example: C:\Program Files (x86)\Microsoft Dynamics\GP2010\Version11.0.1761.0Backup\
This dex.ini file in the Data subfolder also records service pack activity: for example: DYNOLD0=C:\Program Files (x86)\Microsoft Dynamics\GP2010$STD\Version11.0.1761.0Backup\Dynamics.dic
Generally using GP will update date/time stamps on various files inside the GP and GP\Data subfolders - such as REPORTS.dic. FORMS.dic, DEX.ini
Note, the date on this main folder reflects the date you installed the GP client on that machine (or when it was subsequently modified as above). The date on this folder will have no relation to when you installed Dynamics GP as whole on the server with its requisite databases.