totze ha'aretz - let the earth bring forth
The wording "bring forth" indicates that G-d referred to matters which had already been in existence, ready to emerge, but had not yet seen the light of day until commanded to do so by G-d.
The matter can be compared to a farmer who sows six grains of corn at the same time only to find that they take root at different times instead of all sprouting simultaneously. The six days of creation described by the Torah report the sequence in which G-d's creative activity became manifest.
This is what the psalmist had in mind, "for He had given a directive and then it materialized" (Tehillim 33:9) David taught us that G-d's directive and its execution as visible fact occurs simultaneously. (Rabbeinu Bachya)