Especially in winters, but even otherwise, plan your visit in a way that you take some other train to KGM, visit the hill stations or whatever, then take 14119 KGM DDN, visit the hill stations near DDN and then some train back to your source.
Planning it the other way round will be catastrophic as 14120 DDN KGM almost always runs heavily delayed by anywhere between 3 hours late to 12 hours. 14119 KGM DDN, on the other hand, is almost always punctual.

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