This depends on how much time you lose per hit in confusion. It's hard to quantify that, so I'll just make a chart.

TIME LOSS PER HIT		TIME LOSS (+) OR SAVE (-) FROM SKIPPING BITTER BERRY
13 seconds				+3.3
12						+2.4
11						+1.4		
10						+0.5
9						-0.5
8						-1.5
7 						-2.4

When determining "time loss per hit," it's important to weigh some fights above others. For example, you're about 45% likely to get your first confusion on Albert's Zubat, but only 2% to get it on the Twins' Ledyba. So if you estimated 10 seconds for Albert and 11 seconds for the Twins, your average time loss would be 10.04 seconds.

This chart does not consider the following situations, which are important but extremely hard to quantify:
- Getting confused twice in the same fight
- Stacking Rage boosts from Leech Life while hitting yourself in confusion

SOURCE: Excel math to determine average # of turns confused