Amey is the main contractor on Area 6 covering the project between junctions 31 and 33 to resurface the road, renew road signs, repair drainage and upgrade safety barriers.
Work started last December and was due to finish at the end of March.
But the timetable was initially revised to a late May completion and has now been put back further to late June finish.
Highways England is blaming the delays on weather and plant problems and has refused to rule out further changes to the timetable.
Highways England Service Delivery Team Leader Aran Nugent, said: “I appreciate this will be frustrating news for drivers, but I’d ask them to bear with us while we complete this important work.
“By taking the extra time now and completing the job to a high standard, we can reduce the likelihood of future repairs.
“The work has taken longer than we anticipated because of various operational issues which has slowed down how quickly we can complete the work.
“Our contractors have had issues with the plant, which supplies the materials, and we also postponed work over the Bank Holiday to help drivers setting off for the half-term break.”
Most of the work, including the speed limit, will be removed by mid-June after this there will be finishing off work using lane closures only.