wow... that sounds a bit dangerous using the car jack alone...
I usually have mine changed in around 45 mins with little to no mess.
First I take care and jack up my car at four points and support it with 4 jack stands so the car will promote drainage to the rear passenger side.
I have a large drain pan that more than covers the distance that the fluid will shoot out.
I remove the drain plug.
As it's draining, I go into the car and take apart the console. (
www.installuniversity.com). The only tricky part is the handbrake, you need to take a flat screwdriver and manipulate it so the handbrake comes completely up. Around 19-20 bolts later (7mm, 13mm, 10mm) I have the console apart with the shifter removed.
The transmission should be drained now down to a light drip if at all. I close it up, go back into the car and pour in 4 bottles of Dexron III oil, as long as it's Dexron III ATF, be it synthetic or not as long as it adheres to this standard and your transmission isn't already on it's way out, IT WILL BE FINE. I'll be switching to Amsoil ATF from Mobil 1 ATF, but I have more than 10k miles on the fluid and about 30 track passes on it this season with a lot of stop/go daily driving and occasional rips.
Once full, I clean up the shifter of the gasket material, put on a new bead of gasket material, and place it back on the transmission with bolts in but not tightened up. While I let that dry a little I remove the drain pan, lower the car off the jacks, pour the old fluid into a disposal can/bottle and do whatever miscellaneous clean up I feel like.
I tighten up all the bolts now, reassemble the console and see that it shifts smooth. I start it up, and try it out.
I'd like to emphasize SAFETY first to anyone doing this. Using the car jack alone is not recommended, I've had one buckle and bend under weight before, so I do not trust those in car, car jacks at all.
Second is on the matter of synthetic transmission fluid, the original story of synthetics destroying blocker rings came from a story of Redline synthetic trashing a vette t-56 and GM not honouring the warranty. This is because Redline is NOT a API approved oil. As it does NOT conform to API standards (which even the cheapest of dino ATF does) there's no telling what is in it that may be harmful to your transmission parts.