John Gill Commentary Haggai 2:18

"Consider, I pray you, from this day and backward, from the four and twentieth day of the ninth [month], since the day that the foundation of Jehovah`s temple was laid, consider it." — Haggai 2:18 (ASV)

Consider now from this day and upward Or forward; for time to come, as the Vulgate Latin version: from the four and twentieth day of the ninth [month] ; before observed, (Haggai 2:10Haggai 2:15) : even from the day that the foundation of the Lord's temple was laid, consider [it] ; not from the time it was first laid after their return upon the proclamation of Cyrus, but from the time they began to clear that foundation, and to build upon it; and which having lain so long neglected, the renewal of it is represented as a fresh laying of it:

now the prophet, as he had directed them to consider what adversity and calamities had attended them from the time of their neglect unto this time; so he would have them particularly observe what blessings they would enjoy from henceforward; by which it would appear how pleasing it was to the Lord that they had begun and were going on with the building.