The short answer: Several hours a week.
The longer answer is quite a bit more complicated than that. The question itself makes the assumption that the maintenance tasks are work. I, personally, have found them to be a way to connect with the tank, rather than something unpleasant that needs to be done. Your mileage may vary.
I’m going to split these into 3 categories; Daily, weekly-ish, and monthly. I’ll only provide a ‘time required’ and a terse description, I’ll go into more detail about each of them in the future.
Daily
- Check pH: 5 minutes. Simple chemistry test.
- Check salinity: 1 minute. Simple measurement.
- Add water: 1 minute. To counter evaporation.
- Feed x2: 5-20 minutes. Depends on what/how you feed them.
- Clean glass: 10 minutes. Uses a magnetic cleaner, so you don’t get your hands wet.
- Inspection: 5 minutes. Make sure everyone is accounted for and looking healthy.
Weekly
- Full chemistry: 30 minutes. All the needed tests to verify that there is no toxic buildup.
- Water change: 1 hour. Remove some of the water and add new water.
- Filter water: 10 minutes + 3 hours: Filter water very slowly.
Monthly
- General maintenance: 30 minutes to an hour. Taking things apart and putting them back together.
Some of these are only necessary with the listed time frames early on. As the tank matures it requires less active monitoring. After a few months you’ll be able to stop checking pH every day, do less frequent water changes, and just get faster at the tasks.
These numbers are also based on my original 29 gallon tank. They are not representative of what my tank currently looks like, a year on.