I wasn't sure what CALENDAR REFORM was, but interesting to read up on it. Sure covers a ton of possible changes to a calendar system!

Today, Joe gives us "impossible" time events that would require CALENDAR REFORM to make them happen. Ah, what I wouldn't give for EIGHT DAYS A WEEK … although I'd probably spend the eighth day goofing off and then wish for a ninth.
I wasn't as keen on LAST WEEK TONIGHT, as it's not the same type of time impossibility as EIGHT DAYS A WEEK. To me, it's simply describing that tonight, we'll go over what happened last week. Yeah?
It was also jarring to get WEEK repeated between two themers. I don't personally mind when a short word, like ONE or IT or UP is repeated in a grid, but to have a key component in the theme duplicated … hmm.
I hadn't heard of A MONTH OF SUNDAYS, but I enjoyed learning about it. Apparently, it means "a very long time," as in a long, boring stretch of days of rest? Heck, I'd take 30 straight days of rest, thank you very much!
Some nice bonuses worked in, WAGES WAR, REVERSI, NAIL GUN, Toni Morrison's incredible "BELOVED" all standouts. I appreciated all these extras, helping hold my attention through the solve.
The short fill … too much crossword glue for my taste. A Monday puzzle ought to be welcoming to novices, sucking them in. TMS for multiple trademarks isn't really used, and EDS, ELOI, AMIE, BLDG, ISO, NON, ETH. The one I object to most is ELOI, as the others are mostly figure-out-able by normal folks. ELOI is more a Maleskan-era throwback to where you could only do crosswords if you memorized these bizarro short answers.
I'd much rather have sacrificed a couple of the long bonuses in order to clean up the fill. Sorry ROD CAREW, but I think it would have been better to break you up into two answers. (I'm sure Twins / Angels fans will disagree!)
The theme reminded me of Mercury, whose day is longer than its year. Would have been awesome to work that into the theme somehow!