I would not expect Jesus/Michael to appear as a fullgrown man because, he comes as a thief in the night and as a thief he has to be here without people recognizing him for a period.
The Day of Jehovah and the return of Jesus, by scriptural references, seem to be two very different occassions.
The "Day of Jehovah" describes global catastrophe...and this is what comes as a thief in the night. According to scripture, The Day of Jehovah starts with the Abomination described at Matthew 24:15. Immediately after this abomination takes place, then shall be great tribulation such as has never been. So, I think this reveals the kickstart of the events.
Even so, those who are searching for truth (like some people I see here) will observe what is lining up to take place and will understand the meanings so as to be able to recognize what this abomination will be. That day will not come as a thief to everyone. 1 Thessolanians 5:4 But ye, brethren, are not in darkness, that that day should overtake you as a thief. For most people it will be a surprise, but some people will be prepared for the event and will recognize the abomination for what it is.
The sign of Jesus does not appear until after a duration of this great tribulation takes place. It sounds to me like its going to be a rough ride and there will be a lot of people who will die during this time. It is not Jesus doing the killing. Matthew 24:29-31 Immediately after this tribulation, the sky is darkened and a sign of Jesus' return will appear in the sky. I cannot find where it actually says that Jesus himself will come back in the flesh and will actually be on the earth. It says that his angels will be the ones to gather the elect, not he himself. (Will the tribulation still be going on while the elect are gathered? I wonder.)
(I can't resolve Jesus as being Michael. I am not sure how the WT explains that, so I really can't discuss it, except to say I don't get it. But that is another topic)