Conquest,
Most operators break out their inspections however. ie. Phase 1-2, then 3-4. The 5 is the biggie. Operations with a mechanic on staff can usually do a 1-2 in a couple of days. I've never heard of 360-380 hours labor, unless you do them all at once. I'll have to check with my MX department as I don't keep up on inspection times, but I think you can alternate the 1-2 and 3-4 every 150 hours. I check the manual next week and either continue this post of PM you.
2000Flyer
Edited to reflect additional information on Phase Inspections
On a Citation:
Phase 1-4, every 24 mo / 300 hours (this can be broken out to do the 1-2 at 150 hrs, 3-4 at 150, then alternate)
Phase 5, every 36 mo / 1200 hours
Phase 6-50, various intervals.
Hope this helps answer your question.
2000flyer