Edit* Maybe most jobs require at least 1 day to finish.
I really wish there were an easy way to tell how long a task will take (on average). Of course it depends on skill for a lot of things, but if something took 1 hour, it would be nice to know that you could have a job size of 10 and it wouldn't really make a difference for scheduling. However, my take is that it is almost never beneficial to set recurring job sizes to more than 1 per workshop.
Speaking of which, one of the nice(ish) things about the system is that if you have 3 different jobs queued for a workshop and the first job finishes in less than a day, the second one will get started. In fact, it seems to set the job in the workshop exactly the way you would do by hand. You can look at the workshop to see what is scheduled.
Which leads me to:
By the way, the topic just reminded me.
I had charcoal making order(refined coal at most 50) which went wrong for no reason, the dwarves keep making new charcoals despite there were alredy 1400 of them.
I had to delete the order and create a new one, that fixed the problem. I don't know if it was a bug or I accidentally changed daily to yearly.
I totally forgot about this, because I avoid it now. If you set a job manually in the workshop, it can screw up the work orders. The way I get around this is that if I want to add a manual job to a workshop, I cancel the work order jobs (in the workshop -- not the work order) first and then add the manual task. This seems to work every time. Similarly, if you remove a work order that is already activated, you have to be careful to cancel the job from the workshop, because it can sometimes just repeat forever. Sorry I didn't think about mentioning that before now!