Yeah, there's really no quick-fix. Partial-repairs will often cause more severe problems in the future. Sealing in rust anaerobically will actually cause it to spread faster. Look up how ferrous-oxide and ferric-oxide work in tandem.
If you don't have 30-minute to sand down the area, just leave it until you can. Use a small 3" sanding-wheel attachment on a drill to reach the irregular surfaces and remove as much as you can. Wire-wheel can reach the crevices that's not flat. Then use this
CRC rust-converter primer to cover the area. Even though it claims "conversion" of rust, that function should only be limited to the small amounts you can't completely remove by grinding/sanding. Then cover with regular sanding-primer before painting.