This trip can be done comfortably in two days with a stopover in Toktogul.
The first day takes you through the mountains and then through a long tunnel. It passes through a wide green valley full of yurts and livestock. There are big herds of horses, sheep, and cattle grazing as far as the eye can see.
The second day passes along some impressive mountains and infinite golden rolling hills.
Day 1: Bishkek to Toktogul
Shared taxis from Bishkek to Toktogul leave from the main street in front of the Western Bus Station. They park on both sides of the big street on the block just east of the bus station, Map Location: 42.884803, 74.569406 .
The shared taxis are usually minivans and can do the 275 km trip in about 5 hours and charge from 500 to 700 som per person.
In Toktogul, the taxis arrive in front of the main bus station, Map Location: 41.878344, 72.942078 .
Day 2: Toktogul to Osh
For this leg there is a marshrutka that leaves from the Toktogul Bus Station at around 07:00. It will leave without being full because it will pickup and drop off people all along the way. The buses are at the back of this station, not in the front with the shared taxis. The shared taxis go back and forth to Bishkek. It is unclear if there are shared taxis to Osh.
The 335 km trip to Osh costs 440 som and takes all day (roughly 07:00 to 16:00). The marshrutka stops at almost every little town along the way and also does pick ups and drop offs in between.
In Osh, the bus ends at the new Central Bus Station at Map Location: 40.562095, 72.770797 .