This depends entirely on operator skill level. If that much time was required to run a hive it would mean a full time commercial beekeeper would be limited to 100 or so hives, but we know they run far more than that.
A lot of skill is required, and sharing duties with a probably unskilled neighbor is more hassle than it's worth. Even if you give her an unskilled task such as checking the feeder, what's the point if she does not know what's going on inside the hive and if the feeder should be re topped or not. If you are checking the hive, the actual inside of the hive, you will be in a position to know if they should be fed, or not.
Very little time is required to run a hive. But a huge amount of time is required to be spent on research during the first 2 or 3 years. Way more than 20 or 30 hours. Properly keeping a hive requires a fair bit of skill and knowledge. Nearly all new beekeepers go in not knowing just how much time needs to be spent on research. A few of them get lucky and things just work out, but lack of time or desire to do the needed research, is why so many new players lose their hives. It is thought around 50% of new beekeepers are out of their hobby inside the first 2 years because the realised they did not have the time and it was way more involved than they thought.
So my recomendation would be 2 or 3 hours a week on research for the first 6 months and after that a lesser amount. A lot less than that actually caring for the hive.
EDIT - Another thing to sonsider with the arrangement you have, is that the neighbor is stumping up the money, in the belief that your end of the bargain is to successfully run the hive, and eventually produce a honey harvest for her. What if the bees die say, 2 years running, because you could not spend the time to gain the required knowledge, and at the end she has fulfilled what is expected of her, ie, putting up the money, but you have been unable to fulfill your end which was to produce a honey crop. Could that damage the neighborly relationship?