Once again time varies from person to person. The generally accepted routine is a 20% water change per month minimum. Some people will change 5% each week, some 10% every other week, some 20% once per month. In one of Randy Holmes-Farley's articles he shows how it doesn't make a difference if you do small changes often or large changes less often. So things like that vary.
I have gotten into a routine that takes about 10-15 minutes max each night plus maybe an hour or two once a week. The hour or two is for mixing up salt water for water changes, mixing up additives, any water testing, cleaning filters, protein skimmer, whether it needs it or not. I don't test my water every day, some people do. I clean out my skimmer when it needs it or once a week. The 10-15 minutes each day is mostly adding top-off water and any additives, checking salinity, make sure all the equipment is operating.
That doesn't include feeding and scraping algae off the glass of the tank. That is done pretty much whenever. I clean the glass almost everytime I look at the tank. While I'm watching the fish I'll move around the magnetic glass cleaner.
Add to that the time I spend on the computer, major tank cleaning days, rearranging rocks, so on.
For me it is truly a hobby not an obsession. Some here will be the first to admit they have become obsessed and it consumes much of their time. Once again individual personality and life style has a lot to do with the time required.
Don't get discouraged, if you enjoy the tropical freshwater fish you have, this is much more enjoyable. There are many people on this forum that have put together nice setups with ALL used low cost equipment. The problem with starting small only exists if you stick with it and want to expand. When you see tanks for sale on these forums there are typically three reasons why, some are upgrading, some are downgrading, some are getting out. You will often see someone selling a 125g (or such) setup less than 1 year old because the hobbyist just isn't into anymore. Usually that person sunk a lot of cash and will only get a partial return on their investment.
Don't let me be a downer, I have had freshwater tanks for over 40years and salt on and off for over 35. The interuptions came mostly because of things like college, grad school, moving a lot. As soon as I settled down the salt tank was back up. In fact the 30g tank I upgraded from is over 20 years old, still holds water, and is still in use.
The book Cully and I suggested has a check list in it, but it may be outdated a bit. Once you look over the book make a list of things you think you will need, post it here, and pretty much everybody will suggest things to remove, things to add, things to change.
Dave