en_tn_lite_do_not_use/num/09/01.md

after they came out from the land of Egypt

Here the word "they" refers to the people of Israel.

at its fixed time of year

AT: "at the time of each year that I have determined"

follow all the regulations, and obey all the decrees​

These two phrases mean basically the same thing and are combined for emphasis. (See: rc://en/ta/man/translate/figs-parallelism)