Easiest way to empty and fill is to buy a small 100GPH fountain pump at lowes. Its in the outdoor garden section with the pond supplies. It will come with a 1/4in and 1/2in adapter. Buy some 1/4 or 1/2 in tubing and attach it to the pump. Drop the pump into the bucket and plug it in. Put the other end of the hose into another bucket and it will drain the entire bucket. To fill it up just do the opposite,put the pump into the new nute mix and the hose intot the 5 gal and pump it in.
As far as the timer goes i have always had a drip system setup in my DWC container where i have more then one plant. I currently have 4 seedsman white widows growing now and the nugs are so big i had to tie EVERY SINGLE BRANCH to support the weight. Even now i have the drip system running even though the roots are far into the water. The dripping water not only airates the water when it breaks the surface but it also keeps your nutes mixed up good because the water is constantly flowing. I started out using the drip system for only 15mins every few hours. It worked fine but just to test it out i ran the drip 24/7 and had AMAZING results. If i where you i would run the drip system 24/7 until the plant is done. You have nothing to lose and eventually they will look like this
Let me know if theres anything else i can do, good luck!!!