I've no idea, but it's a good question. I'm bumping this up as I see horse person M.E. Wolf is logged on - perhaps we can get a definitive answer.
You rang? LOL
Ok, when there was a battlefield or potential engagements there was a portion of the Cavalry that was saddled up ready to ride with a tight girth and all things in place for the rider to mount. The mounted patrol, videttes were posted as fully equipped and marching. In the early part of the war, they were flankers -- outside the line of march watching and scouting to the sides as to lessen side attack surprises. This job was for light Cavalry. Heavy Cavalry was more assigned to Reserves -- "back up." It was like a 'leap frog' type deal - one portion ready and a portion semi-ready (saddled but girth loose, bridle and bit on the saddle and tethered) and some 'at rest' (unsaddled, no bridle-just in halter munching food and drinking water and nap time/rest time). Giving a cascade effect/affect as to give horses a chance of recovery.
Cavalry marches, according to the 1861 Revised Regulations for the Army of the United States, Article: 42 Marches as to assemble armies:
Cavalry departed at 6 o'clock A.M., march 45 minutes, halt 10 minutes to loosen girth, re-seat the saddle, check hooves and shoes and rest the horse. Operating on trumpet calls, the vanguard stops at the same time as the head column; and rear guard keeps a proper distance from the rear. During these halts, the horses have their girths tighten and their hooves inspected yet again. This being repeated every 2 1/2 miles during the first portion of the march and extended to 6 or 7 miles without a halt, alternatively walking and trotting for about 100 minutes (1 hr. 40 min) until a proper halt can be conducted as to allow a break for the troopers and horses. This break is for the men to eat and horses to be rested usually being the middle of the march. This is repeated in the second portion of the march. It is calculated that a column of Cavalry alternatively walking and trotting with the rests every 2 1/2 miles, the Cavalry trooper will get over 6 miles in an hour and that is depending on the condition of the horse.
In the beginning, I saddled a horse, which means bridle, saddle, breast place, crupper, and my own dressing with saber, gauntlets took me 10 minutes. With practice I shaved it to 1 1/2 minutes by stop watch. Mounting a horse, I could 'walk on' and tighten the girth by laying my left leg or right leg to tighten the girth (pre-elastic) and sitting on the cantle, could tighten the over-girth (that portion that helps keep the saddle in place in addition to the girth). This shaving off valuable time.
Hope this assists.
M. E. Wolf