Technically speaking, Loco Change is of shorter duration, since the next locomotive is already ready and awaiting on the adjacent track. Once the original loco is detached and taken to other track, the newer loco can be coupled and then immediately depart from the station.
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Most stations are able to do this "change over" in under 10 minutes and at times in under 6-7 minutes based urgency, crew skill and other miscellaneous activities.
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Loco reversal (from one end of train to another) ideally takes slightly more time since the original loco needs to be detached, traverse the entire length of the rake on the adjacent track and then again re attach to the train. Additionally the "new" front SLR coach will need to be vacated by the guard and locked and then the guard proceeds to the rear SLR.
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All of this is at least expected to take 15 minutes though detachment and attachment can be done simultaneously at the two ends if 2 different locomotives are used.