There are a lot of different ways to incorporate timing into your Tarot readings. Some are more complicated than others, but all of them can work.
You can designate cards in a spread to represent time periods, like last week, this week, and next week.
You can assign seasons to the suits, perhaps winter for the Swords, spring for the Cups, summer for the Wands, and Pentacles for autumn.
If you use the Golden Dawn system, you might follow their astrological assignments to determine when something happened or will happen in the future.
To learn more about that system, take a look at Douglas Gibbs’ excellent tutorial on the subject at Tarot Eon.
Timing might also be determined by the numbers on the cards themselves. Maybe the Major cards could represent months, while the Minors represent weeks.
In that case the Hermit could signify 9 months down the road or in the past, while the 7 of Pentacles would suggest 7 weeks.
Combined with the seasonal suit system, the 7 of Pentacles would then be pointing to the 7th week of winter.
Another way to determine timing in Tarot is to use the spread demonstrated by Lunar Wisdom in the video below.
It’s basically a yes/no spread that she uses to look over periods of one week at a time. I really like it.
Take a look for yourself and try it out.