What is the time period of stanza 1 in "The Road Not Taken" by Robert Frost?

By time period, I'm not sure if you're referring to when the action takes place or to how long it took. Let's think about both questions. First, the only indicator we have of when this action occurs is the word "yellow." This would indicate that the poem occurs during the autumn. Depending on where one lives, the time when leaves change color could be in September or October. In stanza 3 we learn that the action takes place during the morning, but in this stanza our only indicator of time is the word that shows the leaves of the trees are changing color.

As to how long a period of time it took the speaker to make his decision, the only thing we know is that the speaker stood "long." Obviously, this is a relative term. A long time could be years in some contexts, but in the context of this poem, how long would the speaker have stood there? Since he remains standing and does not sit down to consider his two alternatives, we can surmise that the time involved reflects minutes, not hours or days. According to the resource below, workers who have the choice to alternate between standing and sitting should only stand for 30 minutes because they may start to become uncomfortable after that. Certainly if the speaker were contemplating his two options for more than 30 minutes, he would have sat down to make himself more comfortable during his deliberations. In fact, the narrator may have only spent five or ten minutes thinking about his choice, but it seemed like a long time because he was standing still and not moving.

Since this poem is not as much about the literal roads or the literal yellow wood, but rather about their symbolic meaning, the vague term "long" is sufficient to signify that the life decision symbolized by the speaker's choice of "the one less traveled by" was thoroughly considered. In terms of making major life decisions like where to go to college or what profession to pursue, people may take several months or years to arrive at their final choice. Such an amount of time is consistent in terms of mathematical ratios with spending a few minutes deciding on what road to take while on a morning walk.