Pohnpei time is 18 hours ahead of Pacific Coastal time. This means that it is simply 6 hours behind and one day ahead. At 12 noon in California on June 1 it would be 6 AM, June 2 on Pohnpei. The islands do not institute daylight savings time, so between fall and spring, the time difference is 5 hours instead of six. Cars and trucks are available for rent at numerous businesses in Kolonia.
Budget is probably the best.
Ask for Lillian Smith. Taxis can be requested by phone, or they can be waved over on the road. Bicycles are a very useful method of transportation on the island, especially for long stays. Keep in mind that some of the roads are pretty bad, so a mountain bike would probably be the best. Pohnpei's post office is located in downtown Kolonia and is open from 8 am to 4 pm, Monday through Friday.