I'm just starting to culture phyto myself. Once I get this running for a bit and make sure that I can run a few strains without cross contamination or cultures crashing, I'll start culturing zooplankton.
Like Electrobes said, it can be time consuming, but if you set your systems up so workflow is efficient and so that different cultures are ready to be harvested on specific days, it should't take too much time per day to maintain the systems once you have the cycles and rhythms down.
I have a fairly small setup (doing this mostly for fun and in preparation of a potentially larger system down the road), so my current arrangement has me harvesting once a week. I pull off half of the phyto and store it in the fridge to be used during the week while the remainder gets topped off with new salt water and grows out. It's less than half an hour a week including the time it takes for the water to mix. The 'difficult part' is preventing cross contamination, which is really just cleanliness, keeping cultures separate, not keeping more than one culture open at a time (handling one strain through the entire process and cleaning before moving to the next strain), and having separate tools for each strain.
Advanced Aquariest has had a lot of good articles in the Breeders Net section. There was a multi part series about culturing larval foods as well as a plethora of individual articles addressing culturing phytoplankton and zooplankton.
You really need to decide how much money, time, and space you are willing to dedicate to it as well as why you want to do it and balance that against the cost/benefit/availability of buying prepared and cultured foods locally or online.
For me right now it's more about the experimentation and development of the culturing system.