There are a lot of drug development issues that people outside the field (and beginning medicinal chemists) don't think about. A significant one that sounds trivial is how often your wonder drug is going to be taken.
Once a day is the standard, and it's generally what we shoot for unless there's some reason to associate the drug with meals, sleep/wake cycles, or the like. People can remember to take something once a day - well, they remember it better than most of the other dosing schedules, anyway. That's why you actually want your compounds to be metabolized and cleared - everything has to be ready for the next dose tomorrow.
If your compound has a long half-life in the body after dosing, you'll step on the tail end of the last dose and you can see gradual accumulation of the drug in plasma or other tissues. And that's almost always a bad thing, because eventually every drug in the world is going to do something that you don't want. All you have to do is get the concentration up too high for too long (and figuring out what's too high and what's too long is the one-sentence job description of a toxicologist). If you stairstep your way up with accumulating doses, you'll get there in the end.
Ah, you might say, then just take the drug every other day. Simple! Sorry. Every other day (or every three, or four) is a complete nightmare for patient compliance. People lose track, and doctors know it. You'd better have a really compelling reason to go ahead with a weird regiment like that, and if you do, someone's going to seize the chance to come into your market with a once-a-day as soon as they can find one. (The exceptions to this are drugs given in a clinic, like many courses of chemotherapy - but in those cases, someone else is keeping track).
How about more often than once a day (q.d., in the Latin lingo). Well, twice a day (b.i.d. can work if it's morning/night. Three times a day can go with meals, presumably, but people are going to get tired of seeing your pills. More than three times a day? There'd better be a reason, and it had better be good.
So don't be scared as you watch your compounds disappear after giving them to the animals. You want that. Just not too quickly, and not too slowly, either.