John Gill Commentary Ezra 3:4

"And they kept the feast of tabernacles, as it is written, and [offered] the daily burnt-offerings by number, according to the ordinance, as the duty of every day required;" — Ezra 3:4 (ASV)

They kept also the feast of tabernacles, as it is written
According to the rules prescribed for the observation of it in (Leviticus 23:34–42) this began on the fifteenth day of the seventh month:

and offered the daily burnt offerings by number, according to the
custom, as the duty of every day required ;
for on all the eight days of the feast there was a certain number of sacrifices fixed for every day; and exactly according to the law concerning them did they offer them at this time; see (Numbers 29:12–38) .