It is possible to increase the limit to hours by re-encoding the audio.
As the primary purpose of the service is transcription, you can use voice codec and bitrate.
For example, a command to get exactly what you want.
ffmpeg -i audio.mp3 -vn -map_metadata -1 -ac 1 -c:a libopus -b:a 12k -application voip audio.ogg
Opus is one of the highest quality audio encoders at low bitrates, and is supported by Whisper in ogg container.
Silence detection: also a useful tool.