So, you need to be in Siem Reap on the 13th to meet up with your friends (just so everyone following along is up to speed).
When I arrive early on the 12th in PP, I have a choice between spending a day in PP (booking a room for half a day and leaving by night bus), sleeping in PP and taking the bus to SR the next morning, or hiring a driver to head up to SR with a nice little stop and maybe sleeping in Kampong Thom or Kampong Chhnang, then continuing to SR on the 13th
I’d skip the option with the "nice little stops"—they won’t be that nice given the timing. I’d go with spending the night in Phnom Penh and taking the bus the next morning.
On the 12th, visit the Royal Palace and the Silver Pagoda OR Tuol Sleng, then do the reverse on the 28th or 29th.
Just FYI, here are a few bus companies for the 13th, but there are others. No matter the departure time, I’d advise against booking your seat in advance online. First, it’s unnecessary given the number of daily departures, and second, if you book through a local agency, the company will often pick you up for free from your hotel to take you to the bus departure point.
https://vireakbuntham.com/bus-list
https://larrytabus.com/schedules/phnom-penh-to-siem-reap
https://giantibis.com/book?origin=1&destination=15&departure_date=14-01-2026&trip_type=one-way&passenger_count=1Kampong Cham, where I’ll spend 2 nights—1 on the island and 1 on the riverbank.
The only guesthouse I saw on Koh Pen was super basic, and I’m not sure it’s still there. Erwanploz might know more. Anyway, I don’t think staying in two different places 3 km apart in two days is a great idea. Use the town as your base and rent a bike to explore the island and the paths along the east bank of the river.
For sights a bit farther out, you can hire a motodop for half a day—they’ll know where to take you.
But with only 2 nights in Kampong Cham, you won’t have time for all these trips.
I’ll continue to Kampot and Kep: maybe 2 nights in Kampot, 2 in Kep, and 1 in Tonsay
I wouldn’t split your time between both. In your case, I’d choose Kep since it’ll be your last chance for a beach.
So here’s how I’d plan the itinerary:
Phnom Penh – 1 night
Siem Reap – 6 nights
Kompong Thom – 2 nights
Kampong Cham – 3 nights
Kep – 4 nights (including Tonsay)
Phnom Penh – 1 night
Average of 1.83 full days per stop—much more relaxed than your previous version in the other thread.