MB warrantee time was over 5 hours, maybe 5.5. A good tech can make money doing it in that time. Anyone doing it for less doesn't know what they are doing.
I just looked at Alldata and they claim warrantee time is 5.9 hours and their time is 8.3. Two and a half hours isn't enough compensation for one head let alone two and you surely would do both.
Bosch Master, ASE Master, L1
33 years MB technician