I do oil and it takes from 1-2 hours to do it right, more toward and hour and a half. It also requires changing the filter, pump screen and nozzle. So figure the local hourly labor rate x 2 hrs plus the cost of the basic parts. Unfortunately you will find a lot of companies either rush it or way under price it.
Took this refer man 4 hours to do his, but i had to run to supply house for parts, pluss it was all plugged up after 5 years with no service. I recommend you have it serviced properly to save on energy, i can see my consumption has went down.
Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced