Quite a bit of time?
If your 180 is empty it's gonna take a whopping what? 45 sec to hit water level (1/2-2/3 full sump) Even on the low side of your turnover you're 120 GPM. So dwell time might not be that much but it's compensated by the number of times it contacts the bio. It's a double edged sword.
I know filtration is hard to judge with turnover as you never know the path the water will take. I just go by how long it would take to fill the sump if empty. The reactors I use would take 6 minutes EACH to fill if empty.
Long story short there's 157 ways to skin a chipmunk and there's likely even more ways to do a filter. The only way you're ever going to know what works best is to experiment. Try something, if it works improve it. IF it sucks improve it. After a few years of improvements you'll KNOW what works best for you. Some people will go buy a fancy filter and call it good, and others (like me) will spend years and years making improvements striving for a filter that doesn't need improvements, and incorporates all the different kinds of media since apparently people can't agree on what works best, so it's argued that the "best" way is to use them ALL (submerged rings, bio reactor (K1) and bio ball/pot scrubbie bio towers.
Does anyone remember the Flower on roids from across seas? The "Sakura" that was raised in rediculous amounts of current and in turn was just ripped, VERY muscular. I don't think anyone here is gonna say rediculous turnover is a bad thing, but it's up to you how much cheeze you wanna give the electric company every month.
With rays in general it's nothing more then a gracefull balance between what is needed to keep them healthy and what is wastefull. I wish I knew where to draw the line... I'm into the electric company for $460/mo and the water bill for last month was 24K gallons.
