Albert Barnes Commentary Psalms 104:27

"These wait all for thee, That thou mayest give them their food in due season." — Psalms 104:27 (ASV)

These wait all upon you - That is, these are all dependent on you. It does not, of course, mean that they “wait” in the sense that they are conscious of their dependence on God, but that they are “actually” dependent. The original word implies the idea of “expecting” or “hoping,” and is so rendered in the Septuagint and Vulgate. They have no other ground of expectation or hope but in you.

That you may give them their meat in due season - Their food at the proper time. That is, they are constantly dependent on you, that you may give them food from day to day. Perhaps there is also the idea that they do not lay up or hoard anything; or that they cannot anticipate their own needs, but must receive from one day to another all that they want directly from God.