The 25 hours is the total length of the lessons, so at roughly an hour a day on weekdays you're looking at about five weeks. A month and a bit is realistic. Weekends or a couple of longer sessions bring it down.
On going straight through versus skipping around: I'd do the first two modules in order, because they cover the fundamentals and how to prompt well, and everything after builds on that. After those, it's fine to jump to the modules that matter for your job and come back to the rest later.
A few things that help when time is tight:
- Do one lesson a day and finish it, rather than half of three.
- Do the short exercise after each lesson, since that's where it sticks.
- Your progress is saved, so you can stop and continue with the Continue button on your courses list.
There's no deadline, so a slow and steady pace is completely fine.