All Mailbox Settings are stored in Active directory and once you make changes like Storage Quota limits etc it will take 2 hours to reflect for the user. This is because Exchange Cache active directory information every 2 hours. This is known has Mailbox Cache Age Limit. We can change registry settings to reflect the Mailbox settings (Storage) ASAP.  Recommended modification to keep Mailbox Cache Age limit to 1 hour from 2 hours and its also not recommended to limit less then 20 Min

Details description of the registery settings is describited in the below mentioned site

http://technet.microsoft.com/en-us/library/bb684892.aspx

1. Start the registry editor on your Exchange 2007 Mailbox server
2. Locate the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem key.
3. Create the “Reread Logon Quotas Interval” value
   1. Right-click ParametersSystem, select New, and then select DWORD value.
   2. Name the new DWORD value “Reread Logon Quotas Interval”.
   3. Right-click Reread Logon Quotas Interval, and then click Modify.
   4. Enter a decimal value of 1200 seconds (20 minutes)
4. Create the “Mailbox Cache Age Limit” value
   1. Right-click ParametersSystem, select New, and then select DWORD value.
   2. Name the new DWORD value “Mailbox Cache Age Limit”.
   3. Right-click Mailbox Cache Age Limit, and then click Modify.
   4. Enter a decimal value of 20 (20 minutes)
5. Locate the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchange ADAccess key.
6. Create the “CacheTTLUser” value
   1. Right-click MSExchange ADAccess, select New, and then select Key.
   2. Name the new key Instance0.
   3. Right-click Instance0, select New, and then select DWORD value.
   4. Name the new DWORD value “CacheTTLUser”.
   5. Right-click CacheTTLUser, and then click Modify.
   6. Enter a decimal value of 300 (5 minutes)
7. Restart Information Store service to bring the change in Effect Immediately on all the Mailbox store server.