Feeding on the aspen isn't the best, but lots of people do it; you can minimize the chance of the snake ingesting the aspen by placing the food in a shallow dish, or on a piecec of newspaper or such. If you only have one snake, I'd take the time to put it in a "feeding tub" to rule out the risk. Any old container will work, frrom a paper bag, to a "tupperware" container. If you do this, be absolutely certain that the snake can't escape; if you plan to leave it in this container overnight also ensure it has ventilation.
You should leave her with the food for no more than 8 hours, IMHO. I'm assuming you are feeding frozen/thawed rodents, if you aren't you should be. If you leave the snake with food overnight and it hasn't eaten then you don't want to let it because the bacteria levels on/in the food item are getting high enough to make your snake ill. If this happens do not try to feed for a mimimum of 4 or 5 days - you don't want to build a negative feeding responce.
You can feed any time of day, but many snakes seem to prefer to eat in the evening or at dusk. Corn snakes do not have nocturnal eyes but I don't think they are strictly dirunal either.
so to sumarize:
1. get some frozen mice, or euthenize and freeze your food a week in advance (freezing kills many pathogens and paracites, and also renders the food more digestible.)
2. thaw the food in some hot tap water. 5-10 minutes for pinkies, and up to 30 minutes or more for large mice/small rats.
3. pat the food dry. careful: the freezing weakens the cellular structure, so if you push or squeeze too much you can tear the flesh or something else that will be graphic and probably unpleasant
4. place the food into the feeding container.
5. wash your hands.
6. gently retrieve your snake, and placee then into the feeding bin. secure the bin to prevent escape.
9 times out of ten the snake will be eating before you know it. If you have a very large feeding bin, place the food at the edge, not the center - the snake will find it faster this way. If you have a regular feeding pattern and the snake starts to avoid the food, this may be a sign of illness, or stress, or possibly even that the snake is "in heat" or even "in shed". You'll get a hang for it with time!
^Curtis