I would use a button interface that will let you know how long I took. Its easy to know if it was more than 60 minutes, specially if it does not requires how many minutes after the 60 mark.
Expanding in the subject, here is my input:
Although 60 minutes time frame is a great push and pressure to complete the challenge, I think that time frame is not for first timers due to the following reasons:
I can imagine that most of the practitioners or designers in this field will have a visual learning method, but most likely there are several learning ways among all the participants. There are many that like to write things down and more so when there is no indication of how long the participant will have access to the lessons for future references. (In that way won't have to take notes. Not so for the ones that learn writing things down). Besides, if one would like to keep what is seeing needs to capture it and initiate an archive system to review and study or use it eventually for further projects during the program. Another delay completing the stages may occur according to the amount of knowledge about the subject, adding to that the interest in wanting to explore creating a not so typical output, taking advantage of the tools provided. Never mind daily schedules...
Academically speaking, the practice to learn technique will need a few other tools handy, as well as indications, so the participant will feel safe and secure to go on lesson by lesson not taking notes or worrying about where to find the details for reference, (some generic way that would apply), to finish the last stage of the challenge. Even if one can go back to look for details -since for a first timer would be hard to remember a code, not sure all others can either- the details are not made to be extracted/copied and place at the text editor. Then, for first timers taking notes or saving code details somehow (organized) is a most for future reference. Which it most likely delays the time frame for completion.
I am sure creators have taken this in consideration, but I answered in case the 60 minutes indication for completion maybe can be looked at some other way, or provide other tools to make it be completed in 60 minutes.
I have no objection with 60 minutes or 1 hr indication. When is 60 minutes it reminds me when script/screen writing for film that each page is equivalent to a minute and it made me think of a lesson per minute, which it would be reasonable if one can be sure that what learned it will be there to return to it -organized- for reference.
There are some skills references provided in case of need, but are not in the same way they've being applied which is what one wants. One can find the exact way, most likely, in w3schools that apply more to the need in time.
Nevertheless, 60 minutes or not, I finish each challenge the best way I can in order to retain the information. For me is more important to retain information regardless of all the references available, than pass a challenge and then later on encounter a tiny little thing that detains me and I can't figure it out cause I would not know how to debug it.