It can be time-consuming, but it doesn’t have to be. I would allow one hour per week per hive in spring and summer. In autumn and winter, one hour per month is probably plenty. You will probably need double that time for the first few months, while you get confidence in what to look for when inspecting a hive. However, once you have some experience, it gets faster.
Extracting honey can be messy and time-consuming when you start out, if you don’t have a Flow hive. For me, I would say it about an extra 4-8 hours per hive per season. There are plenty of members of this forum who are much faster than me, but I like to take my time and do it the way I think is best for my hives and my honey. For a Flow hive, your “active” time extracting (when you are actually doing something physical) is probably around 30 minutes per hive per season. Much quicker and cleaner.
Hope that gives you an idea. We have a lot of UK members, so maybe some of them will add to what I have written.