Never done a retube on a M777; after my time in the Army. On a M198 towed 155mm howitzer, direct support maintenance could do the job in a day or 2, if authorized and if parts are on hand. Still is typically a depot level job. Again a day or two. Normally, we would get a howitzer to replace one going to depot maintenance so that we kept our combat readiness. Recoil mechanism on the 777 looks more complicated than M198, so retube might take a little longer. Still days, not weeks, assuming barrels and mechanics are available.
So two days from now this article will become obsolete.
Please read 68 and 77, and adjust for local combat conditions.