This question depends entirely if you are planning on doing the repair yourself or taking it to a shop. If you do decide to replace your 4.6 intake manifold independently, the timeline depends on your experience. If you have a fair bit of technical experience, the job should take between 3-4 hours. However, if it is your first time working on your vehicle it could take twice as long. Certified Ford mechanics generally charge around 3 hours of labor to complete the job. It usually doesn't actually take them that long to perform the repair, though.