Maybe try a practice run. Stick one end in some water and the other in an empty container, let it run for 24 hours and see how much it doses.
If you set it to, for example, 500ml dosed over the course of the day, and after 24 hours it moved 500ml of water, then I wouldn't get too hung up on the time being all over the place. If it's skipping doses, that's a problem, if it's dosing 20 minutes later than it should, it's annoying, but not a huge deal.
Don't get me wrong, it's not how it should be and you have every right to be angry when something you bought doesn't perform as advertised, but it'll get the job done while you're out of the house for a day here and there.
Also, it'll give you a good excuse to buy a second one in a few months when you're looking to throw some money at the tank. You can buy yourself a better one and put this one in storage as a backup or to use for something less important (ie I have a pump I repurposed to keep a drain line flushed so doesn't really matter how well it keeps time).