To your questions;
I think the rating-categorization is generously okay. I mean we're not even much yet we have 4 tiers.. that imbalance of "effortless win" and "unfair competition" can't be offset given the broad difference between our individual ratings, so I'd say that part is okay.
Regarding the length: it's okay for me actually... It's a means to relax after having a long serious week. I mean time passes by so quickly you wouldn't even be counting how many rounds left. That said, I think a shorter duration either more that one round a week or lesser number of rounds will give it more "life."
That brings us to the last part: time of the day. I believe this one is outside your control.. it's either too late for someone somewhere or cutting into someone's schedule. I missed some days and preformed really badly in some because of business and I still can't even suggest a better time. Life can be really unpredictable.
P S (edit): What if moving forward there's individual tournament for all 4-tiers??
Like, instead of having a 1300 face-off some 2500.. there's a separate tournament for <1500, 1500- 1799.. all happening at the same time for the same duration?
Thanks for your feedback! Appreciated!