cook assembled lasagna now or later on..closer to dinner time?

Lasagna definately benifits by a nice resting period. All the flavors meld and any excess liquid gets sucked up so slicing is easier and your pieces look cleaner. BUT...... I would just be wary of the "danger zone" of bacterial growth in food. If your food sits in the danger zone (41 degrees F to 140 degrees F) for 4 hours, you are breeding bacteria at an alarming rate. Putting a hot lasagna in the fridge early in the day and then re-heating it later is a good way to do that. Its just not enough time to bring the lasagna down to a safe temperature.

1) If you plan on cooking and serving on the same day, bake your lasagna so that you have time to let it sit on the counter for between 30 minutes and an hour. That will be enough time to let your lasagna come together without any safety issues.

2) If you can, bake it the day before so that it will chill properly in the refridgerator. Then, just re-heat the next day before serving.

I would cook it, then cool it and reheat later. Lasagna does very well that way - the cooling period melds the layers together so they don't slide off each other as readily when it's reheated.