For an adult Corn, I reckon about half an hour to feed/thorough spot-clean of poop/change water, once every 10-14 days (longer if they're a fussy eater or take their time). After that, a couple of minutes every 2-3 days to change water, and 5 minutes every 10-14 days to spot-clean.
The full bedding change/disinfect of a viv takes me around an hour for a full-sized three foot one. Hatchling tanks are much easier - quick squirt of reptile disinfectant & a rinse under the shower.