It really depends on the secondary. Some have many essays, some have none. A lot of secondaries have the same essay(s) so you can just re-use them and speed things along.
How long would it take you to a write 1500 word essay of "describe an ethical dilemma you have faced" or "describe a situation when you have genuinely helped someone" or "how have your life experiences led you to pursue a career in medicine?", etc. However long that would be is how long it takes to complete a secondary.
Yes, UPenn and Mayo clinic have a "send in a check for 100 dollars" secondary. Whereas, UC Davis and Duke have about 8-10 essays in the range of: "Where do you see yourself as a Physician in 10 years?" "Describe your leadership experience and how it has affected you" essays that can take 2 weeks.