Always behind is spot on about working at the pace for that individual horse. There are those that do get mentally fried faster and need to be taught slow & easy and there are others that thrive when challenged constantly.
Depends completely on individual trainer and horse, like almost everything horse it's always an individuals assessment not a generalized standard. I will say that 30 days does not make a broke horse. I look at the first 30 as laying a foundation to build on, kinda like pre-school, giving them the concepts that they will need to be successful when they do start real schooling. I personally don't like to take horses for just 30 days and rarely do. I will take them in for just 30 days if they have had the groundwork & basics leading up to riding under their belt & going into competent hands for finishing or if it's a tune-up on a finished horse. If it's a barely halter broke, completely green horse I prefer not to. Simply because there is so much that needs to be done on the ground before that first ride and owners get frustrated when you aren't on their horse straight away.
That being said with my own personal horses & those that have the ground work under their belt - at the end of the first 30 days I expect them to stand quiet to mount/dismount, flex and bend, begin to understand and respond to leg pressure & yielding, be "on" the bit, give me their nose, full understanding of whoa, one rein stops & back a few steps quietly. Everything has to be mastered at the walk before we trot and at the trot before we lope. Most of them at the end of 30 days here are ready to go out for a trail ride (something I do myself with all trainees before sending them home) but are generally nowhere near showpen ready.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.