This explanation comes from something I read about Albert Einstein.
So this explanation starts with us standing on an underground Subway Platform. The train tracks are in front of us. All of this is a representation of time, physical and spiritual.
Now as we stand there, a Subway Train is passing by. The cars that have passed by represent the past….the cars that are coming towards us are the future…and the car that is in front of us is the present.
Now as we stand there Yeshua stroll up and greets us. He is with us in the present. He grins and points at the Subway Train and says, “I am there.”
We look, and as the cars pass we see Yeshua, Yahweh, and the Holy Spirit in the windows of every car, past, present, and future. Illustrating that the Trinity exists fully in the present, but to some degree or extent the Trinity exists in time past and future. This is the natural reality of the Gods and time…so…
Yeshua was born the real Son of God and as such when He was conceived of God, He then perceived time and existed in time, just as Yahweh and the Holy Spirit do.
So to some degree Yeshua was present in the Old Testament but not to the extent that He would be performing miracles or be referenced by name in the Old Testament scriptures. In other words, there is no scriptures in the Old Testament about Yahweh talking to His Son or telling His Son to do something, or that He even had a Son that was a God. Or that Yeshua actually physically did anything in the Old Testament.