Salesforce getUpdated() SOAP method

Retrieves updated records for the specific time interval.
The date range for the returned results is no more than 30 days previous to the day the call is executed.

getUpdated("Account", StartTime, EndTime)

Following is the reference link

There is a limit of 600,000 IDs in the result GetUpdatedResult[]. If your getUpdated() call returns more than 600,000 IDs, an exception EXCEEDED_ID_LIMIT is returned. You can correct the error by choosing start and end dates that are closer together.