Is Ostbahnhof your final destination? If so don't even worry about this since there's different trains that leave like every 20-30min depending on the schedule. Note that the FEX (Flughafen/airport Express) currently does not serve Ostkreuz (not Ostbahnhof) this month. You can take both the RB (Regionalbahn) and S-Bahn where the former would be the preferred and faster option.