It’s normal for me to leave it either overnight or, at least, as long as possible the same day (for example if there are small children or pets around who may not understand it’s not for them).
Some spirits like Belial may occasionally ask for the food to be left until it goes distinctly rotten, but there is no need to do this unless asked, and even those spirits are unlikely to be offended if this is not possible or if you cannot yet communicate, others may be offended by the same thing, so when in doubt, dispose of it within 24 hours.
There is a method of de-linking any energy from the offering after you have removed it for disposal described here: Tutorial : Tool-Free Magick Using Your Hands.
The simplest method of disposal is to wrap it in some clean kitchen towel, or other clean paper, and place it in the ordinary trash or in the composting bin/compost heap.
Don’t flush things down the toilet unless you have no alternative, this may seem disrespectful, and pour any drinks down the kitchen sink if possible, and not the bathroom or toilet washbasins for the same reason.
If the spirit has an elemental connection (earth, fire, etc.) you could dispose of the offering into that element, by burying it, or pouring it onto the earth or into a watercourse, burning it, or for air, pouring it into your hand then casting it through the air (like farmers do with seeds).
Obviously that might not always be appropriate but it’s one to consider, with the final statement of “I commit this offering to your element, (Spirit’s name), of air/fire/water/earth.”
Do some divination on whether that’s appropriate of course, but it honours the spirit whilst disposing of it in a suitable way.
If they don’t have an elemental attribution, bury it, or maybe leave it out if it’s edible - but please don’t leave out anything with chocolate, raisins, sultanas, current, or grapes, they’re highly toxic to a lot of animals. 
Of all of these, I usually just wrap things in clean kitchen roll and compost them, and would only prance about at crossroads or playing with elements for something very special, because life is busy and if my mind attaches “it’s complicated” to offerings, that is a disincentive to making them as often as I may otherwise do. 
