There are normally two buses leaving daily from Kathmandu/Pokhara to Chitwan where price differs as per their services:
Deluxe Air Condition Buses:
Bus leaves from Kathmandu/Pokhara at 07:00 AM and reach Sauraha around 12:30 Pm where it will stop one station for Breakfast. Seats of these buses are comfort compared to other ones.
Standard Non Air Condition Tourist Buses:
These buses leaving time is also same like Deluxe bus however if you are looking for cheap option than this might be your travel partner to your destination.