Jamieson, Fausset and Brown on Ezra 3:3

3. they set the altar upon his bases--They reared it upon its old foundation, so that it occupied as nearly as possible the site on which it had formerly stood.

they offered burnt offerings ... morning and evening--Deeming it their duty to perform the public rites of religion, they did not wait till the temple should be rebuilt and dedicated; but, at the outset, they resumed the daily service prescribed by the law (Ex 29:38, 39; Le 6:9, 11), as well as observed the annual seasons of solemn observance.