Here’s some information I received from a resident of Sarteneja in 2010:
"Buses depart from the Swing Bridge (NOT the bus terminal) in Belize City on Monday to Friday at 10:30 am, 12:00 noon, 4:00 pm, 5:00 pm. On Saturdays, buses depart at 10:30 am, 12:00 noon, 4:00 pm. No bus on Sundays.
Same bus passes through Orange Walk, stopping across from the St. Christopher Hotel (NOT the bus terminal). Departure time from Orange Walk is about 1.5 hours after departure time from Belize City."
Your schedule has one more bus (at 2pm) than mine. Do you know if your schedule is before or after 2010?
After buses leave Belize City, they will take about 15 minutes to reach Ladyville. I don't know if there's a scheduled stop at Ladyville, so you have to wait on the side of the highway and wave an arm up & down when you see a bus coming. Be aware that there might be other buses, so make sure you get the Sarteneja bus. A sign should be in the front window of the bus. I don't know if the bus line is Perez.