The scriptures allude to a beginning point, the start, which was the creation of Jesus Christ. Prior to that it is called time indefinite, showing that time was not defined yet, and it is a perfect description of a dimension where time does not exist. When does eternity begin or end? Eternity, in the fullest sense of the word, cannot be defined by time, but rather time falls within eternity. Somewhere within Gods existence he began creating, thus the stream of time which we, and the angels are a part of, began.
I'm not certain angels are exempt from time and space, possibly they just fully understand how to use it, which might seem as though they are exempt. Angels certainly understand everything about this universe and how it was created, therefore they have the knowledge to manipulate it to a degree that we may one day ourselves understand. Because they too were created within the stream of time that began with Jesus Christ, I doubt they themselves have the ability to time travel along that stream of time, but must ride it out as we all do. The ability to see forward or backward on that stream of time is limited to Jehovah and anybody he wants to show. I could be wrong, but allowing any creation to go forward or backward in time would undermine the essence of free will, and merely create an infinite amount of variables that would have to be contended with. I just don't see it as something Jehovah would allow. Besides how else is it that only Jehovah knows that day or hour, if angels were exempt from time?
“. . .From time indefinite I was installed, from the start, from times earlier than the earth. 24 When there were no watery deeps I was brought forth as with labor pains, when there were no springs heavily charged with water.” Pr 8:23-24
“17 Now to the King of eternity, incorruptible, invisible, [the] only God, be honor and glory forever and ever. Amen.” 1Ti 1:17
I'm not certain regarding the comparison between time being created and how that supports a triune eternal godhead made up of Father, son, holy spirit. The verse I provided in Proverbs actually shows just the opposite, in that Gods first creation, Jesus Christ portrayed as wisdom, had a start which would not be possible if he was coeternal with the father.