I believe there's a coin flip for the 3rd, 4th, and 5th round picks this year (could be wrong on the numbers). When will this flip take place? Thanks.

usually takes place at the combine.

Here is some info about the flip:

 

Because the Chiefs finished third in the AFC West with a better record in common games over the Raiders, Oakland will draft ahead of them.

 

So the Falcons and Raiders will flip a coin for the third spot. If Atlanta wins, it will pick third followed by Oakland and Kansas City. If Oakland wins the toss, then the Chiefs and Falcons will flip for the fourth spot.

 

Also, like BearSox said, the flip occurs at the Combine.