Question

I shall be telling this with a sigh somewhere ages and ages hence: two roads diverged in a wood, and i— i took the one less traveled by, and that has made all the difference..What time is he thinking of in the last stanza

Answer 1

he is thinking of the time when he will be old and will tell his future generations about how he made his decision

Answer 2

the speaker is telling us about what he's going to say in the future. From where he is now, just looking down the path as far as he can see, he can't tell if the future that it leads him to is going to be good or bad. He just knows that his choice is important – that it will make all the difference in his life.