I think one of your calipers may be sticking causing the lessened effect when cold.
First, on modern braking systems, you should open the bleeder to expel excess brake fluid when retracting the piston. It serves to reduce the propensity for pushing debris backwards through critical areas like seals and ABS components. Then only retract the piston far enough to fit the new pads over the rotor or you risk pushing the piston seal through a historical crud line that builds up over time. This can damage the piston seal.
Secondly, you should never need to add fluid in between service intervals. This is a good way to see if your pads are worn to the point of needing replacement by looking at the fluid level. If you need to add fluid, you have a leak that needs to be addressed separately.
Third, it is probably too late now but you really need to clean up spilled brake fluid immediately. It is one of the best known paint removers.
Fourth, when you go to set the pads after the re-installation, use very short strokes of the brake pedal. Under no circumstances should you purposely press the pedal to the floor. This can result in a similar scenario in the master cylinder as the caliper piston when pushed too far back.
Lastly, did you grease the sliders to ensure the caliper is sliding properly?