We can praise, praise, praise ... God inhabits the praises of His people.
When we move from praise into worship, we're moving to the next step ... worship. This is where most churches miss it. It cannot be formatted to where the worship leader announces, "OK, we're finished praising ... now we are going to enter into worship."
No, the music itself should transition us from one to the other ... the praise flowing into worship, and by it being announced verbally, the flow stops.
Praise doesn't have to be a fixed amount of time because the determining of it is by the individual person participating in the praise that leads into the worship. The musicians are supposed to lead us in praise and then move into worship.
Some "worship leaders" try to categorize and control this time by the clock. When the Holy Spirit is involved, the clock shouldn't have anything to do with it ... but when this time is ruled by the clock, take the clock away.
Reverend Robert W. & Mary C. Butler