Kent, The slow bed heat up time is just a fact of life with a 12V supply and the resistance of the bed that you are using. You can only pump in so many Watts at 12V. My Robo3D takes a few minutes to heat up to 110C for ABS with it’s 12V supply. I know that other’s have upgraded to 24V but I did not think it was worth it because I don’t use ABS much anymore. I usually keep my bed at 80C or so for PETG or 50C for PLA.
I did the Marlin PID tuning process but don’t think it sped up heating much.