I am considering using a disposable foil plate to bake banana bread. Is this advisable or can it be harmful? If it is acceptable, how will I amend the temperature and cooking time versus the original 350°F, 55 minutes.
Quick breads in disposable foil is the lifeblood of bake sales across the land.
There are loaf sized foil pans you can use. The 'plate' that you mention sounds like a pie-plate, which would make a very different shape and therefore baking time.
If you use a loaf pan that looks like a regular steel or aluminun pan, then your cooking time,etc will be very similar. I would advise checking it 5 minutes earlier than you are used to, as the thin pan will allow faster energy transfer.
When you ask about 'amending your temperature and cooking time' what you are really saying is "when is it done". To use the bread pan tray (on the linked page above) if you are 'normally' using a metal bread pan I should think no changes are in order. If you are changing from a glass bread pan then you should either drop your temp 25°F or reduce your cooking time by 25%... then start checking for 'doneness'. When checking to see if a banana bread is done you can use the 'old reliable' toothpick test (does a toothpick come out clean?) or you can check the internal temperature for 200° F.
There are a handful of other variables from your oven to brand/type of flour you use that could also have minor impacts on the product, I would make a couple as experiments as your mileage may vary.
I have baked a cranberry quick bread in lots of different pans. It always works and is very forgiving of the cooking time. You can cook it another 30 minutes beyond when it is done with no ill effect. Foil pans versus solid metal pans are not important at all. If the pans are the size you are used to, I would check 10 minutes before you expect it to be done and every 5 minutes after. If they are smaller, I would check earlier. If they are larger, you might drop the temp to 325 or 300 and expect rather longer cooking time, but the results will be good.