Hi @mrear,
Thanks for your question!
To know which intervals to practice, there is a suggested progression in our interval exercise MP3s. You can also read this FAQ about how to know when to move on with which intervals you are training.
Intervals are a good way to develop your relative pitch, but if your main goal is to play chord progressions by ear on guitar, you may not want to spend too long purely on intervals. I would actually recommend you start with this video tutorial series on playing guitar by ear. That will give you a good idea of what kinds of interval and chord skills you need to develop, and then you can come back and decide how to train them.
Regarding how much time to spend daily, there’s more information here, but yes, 10-15 minutes per day should be enough to see improvement over the course of a few weeks, particularly if you keep your training focused. That means that 10 minutes on interval recognition is better than 3 minutes on intervals, 3 on chords, 4 on rhythm, etc.!
Does that help?