If you added your Earthlink account to Gmail, then it's perfectly normal.
POP accounts are polled about every half hour, sometimes more, sometimes less depending on google's history of finding mail in the POP account.

From inside gmail, you can hit settings, accounts, and "check mail now" for that account if you want it to poll right away. But you don't have an option to increase the polling frequency of non-gmail accounts via POP.