I'd say Sea World is about 20-25 min from the MK. You should be good for an afternoon break.
But if you are planning on returning back to the MK after your break, factor time of getting in and out of the MK park itself. First you have to drive to the Ticket & Transportation Center (MK parking lot), get a tram from your car after you've parked and it will take u to either the monorail or ferry which will then take you directly into the park. The parking/tram/monorail or ferry can be anywhere from 25-45 min in time. Then factor in the driving to and from your hotel (maybe 20-25 min each way). So, if u decide to return back to the MK after your break, you could conceivably be looking at a total of anywhere from 45 min to an hour from the time you leave your hotel to the time you step foot back in the MK park. The MK park is the only WDW theme park that really involves the most steps and time. Getting back into Epcot or Disney Hollywood Studios would take less time.
Oh...and WELCOME to the DIS !