Sissy,
The reason I asked about the filter is if you have a lot of crud to filter from the pond, a sand filter is much easier to clean if you have to do it often during the fill. Sounds like you have a nice pond so use it.
Jo,
As long as the pump is submerged it should get adequate cooling so it could run continuously. When I filled my 22K gal pool in 97 it was an original pump maybe 22 years old. Ran continuously for almost a day as I vaguely recall. Still working fine almost 9 years later. Maybe I shouldn't brag.
Al