You're asking if you rolled a 19 or lower, if the animal would hang out for under 6 hours and sometime during that timeframe you could send him off?
I'd lean towards no, that would be too powerful IMO for a level 1 ritual, even if it's not game-breaking, the ritual seems like as soon as you complete the ritual, you whisper and the animal delivers. Now there may be some wiggle room in the reading that "Once the ritual is complete, you whisper a message of up to 25 words to the animal and name a recipient and a location". If you don't whisper, how long until the animal then leaves? The spell says X hours.... hmmm... let me think on it.