Depends.
Basically, I do not think of the activity as “rehearsing” until I am working to build muscle memory with a technique or to refine my work flow. Thinking about changes, researching changes, experimenting with changes…are all good, and all need to be done…but that is not the same as rehearsal. Perhaps that comes from my background as a competitive dancer. Rehearsal does not start until the choreography is done and learned.
I find that short(er) sessions are better for me. So, given 60 minutes a day to practice, two 30 minute sessions tend to work better for me. That said, anything under about 20 minutes isn’t enough for me to actually accomplish something productive. I do something DJ related 4 to 5 days a week. Sometimes it is just 30 minutes, sometimes it is a couple hours.
I spend time working on my music collection in general. Processing new music into the collection happens every few weeks. I use SoundHound to ID songs I hear while out and pull those that grab my attention into a playlist every couple weeks. I am constantly fidgeting with tags, etc. This is NOT rehearsing.
I spend time building remix sets, and working on my library of sounds for producing. I am currently working on building a remix set that works with Motown and soul and 60’s R&B. This is NOT rehearsing.
My current controller is an “old friend” by now. I have been using it for 3-ish years. Whenever I buy new controllers I “learn” the mapping by experimenting with all the controls and features. It can take a while to figure out how I want to incorporate a new toy into my work flow. This is NOT rehearsing.
I am always experimenting with new techniques. Right now, I am working to incorporate the MF Twister step sequencer into my sets. That means building remix sets that sound good with different genres of music. It means working out patterns/rhythms on the sequencer that sound good with different genres of music. I spent a couple hours working with the MF mappings, and learning all the controls and the feel of the unit. This is NOT rehearsing.
I am a mobile DJ, and I play a WIDE range of genres and tempos. I do not normally use sync, so learning to work with sync is taking some time. So, I am practicing with the MF Twister in my workflow. I have a good idea of how I want to use the tool, and I am practicing toward that specific goal. This is rehearsing.
I practice “quick mixing” techniques with slams and/or with FX. My goal is “ten songs in ten minutes.” I use this technique as a “finale” at weddings to clean up any outstanding requests. So the playlists tend to be a bit…well…“random.” I have a LONG stockpile of these song lists, so I have enough material to let me practice. This is rehearsing.