6:55 AM, Sunday July 19th 2020
DaB is a pretty intensive course and requires a lot of concentration, so 1 page of exercise per day is a good pace to start with. I've been doing that since I started DaB (I've finished Lesson 1 and currently doing 250 Boxes) and it's just about right for me. If I'm feeling fresh and not worn out by that 1 page, I'll do 2 pages, but that's maximum.
Uncomfortable's 50% rule is also a great rule-of-thumb:
https://drawabox.com/lesson/0/2/50percent
Every art session I do, I try to make it half DaB, and half my own art for fun. Sometimes I only have time in the day/evening to do a DaB exercise, but that means the next day I'll start off doing fun art for that session. With my life schedule and responsibilities, and doing fun art, I usually manage 1 page of DaB exercise per day anyway.
If DaB exercises are the only drawing you're doing at all, you're probably grinding and ought to slow down, especially if you're determined to do DaB (and art in general) for the long haul. The 50% rule is less of a "rule" than about developing a mindset of enjoying the art process. Learning is frustrating and DaB lessons are tough, so that frustration has to be balanced out with fun, or we'll all burn out. Grinding runs the risk of you developing an "art = frustrating" mindset. While art can be frustrating, you don't want to lose the sense that "art = fun" too.
I guess you have to reflect on how you're approaching your art. If you find that you're getting worn out or fixated on DaB exercises, you're probably rushing and it's best to slow down.