How much time it takes to merge a 10 mins video for my YouTube Channel?

Short answer is that it depends. If you are merging a HD video then it might take a little longer than the regular video. Also merging is faster when you are on wi-fi compared to when you are on your phone data plan. Then there are other factors like signal strength, connectivity etc. if you a have reasonable internet speed then merging a 10 mins video will just take couple of mins.