I am wondering if the two witnesses will be arriving in the fall, perhaps this year, during the Feast of Tabernacles.

I have a couple reasons for why I am leaning this way.

Right now, we are about to start the Jubilee year in a month or two.  It would then end in the spring of 2017.  The Jubilee year is the 50th year of a count of years.  Though its theme is a new beginning, it is the end of a count of years.  So, I am thinking that the day of the Lord could begin after this Jubilee is finished.  I am hoping that the Jubilee year is when we go home.

I think of the Day of the Lord as a 1000 year "day" thinking in terms of what Peter said to keep in mind, that a day with the Lord is as 1000 years and 1000 years as a day (2 Peter 3:8).

The soon to arrive Day of the Lord will actually start with the seven years of Judgement in my thinking.  Jesus breaking the seals in the first part of Revelation is the start of the process to destroy the already defeated enemy and to refine remnant Israel for their role of ruling and reigning with the Messiah.  This is why as the scriptures describe the coming Day of the Lord, it often describes a time of judgement but there can also be verses that point to a restoration.  The "Day" includes both.

With the witnesses beginning their proclamation possibly this coming fall, it would fit Malachi 4:5 where Elijah is described as arriving before the day of the Lord.  Also, with them possibly starting this fall, their three and a half years of prophesying would end around the time of Passover.  It is my opinion that when the witnesses are described as being dead for three and a half days, then they are resurrected and immediately ascend back to heaven, that this will take place on the anniversary when Jesus did the same.

There are a couple of reasons I think it will be during the Feast of Tabernacles when they start their proclamations dressed in sackclothe (Rev 11:3).

For one, it would echo the possibility of when they showed up with Jesus on the Mount of Transfiguration.  Peter, who was present, offered to build them booths/shelters.  I think he offered this because it was during the Feast of Tabernacles.

Also, when Moses went up to Mount Sinai the first time, it was the 18th day of the third month.  I base this upon the timing clues in the Exodus chapters leading up to this (see Exodus 19:1).  Jewish tradition has this taking place on Pentecost and I do not think this is valid.  The common understanding of when Pentecost takes place would have had Pentecost over for about 10 days by the Israel arrived at Mount Sinai.

Moses was on the Mount alone before God for 40 days the first time.  He then came down with the first set of tablets, broke them, and ended up going back up shortly thereafter to intercede for the nation.

I found out in Moses' account in Deuteronomy (see 9:18), that he actually interceded for 40 days and then went back down.  Exodus does not give this detail.  He then goes back up for a third set of 40 days to have God write the commandments again on the stone plates Moses had to make (God's way of teaching Moses to not break His stuff).

That is a total of 120 days.

When I did a count, using a calendar, and starting with the 18th day of the third month, Moses would have come back down with the second set of tablets in the middle of the Feast of Tabernacles.

In my mind, when might Moses come again in the near future and represent the law to Israel, the law that points them to salvation in Jesus alone?  At the anniversary of the time when he presented the law that second time to Israel years ago, perhaps.

Also, I find it interesting that this matches a time when Jesus went up to the Feast of Tabernacles (see John 7).  At first He went up secretly but in the middle of the Feast He began teaching in the temple (vs 14).  I wonder if this will be what the two witnesses do as well.

Now, on a prior post, I mentioned that there is a possibility that the 144,000 will be sealed by the witnesses during the Feast of Pentecost.  That might happen as soon as this year.  It could also be done Pentecost 2017 but right now I do not think so (I will explain this in yet another post)  My reasoning is that the time to seal and to teach the 144,000 does not have to coincide with the actual amount of time (three and a half years) the two witnesses are prophesying to the nations and Israel proper dressed in mourning clothes. For all I know, Elijah might show up in Israel way back during Passover as Jewish tradition anticipates.  It is an interpretive assumption that the witnesses are only on the earth during the three and a half years of proclamation and that is all.  I do not hold to this as being absolutely necessary.

Douglas Henney