Show optional configuration of MQTT device

Hello, I am new in Home Assitant world. I have created Arduino NANO controled board with 32 buttons (single, double and long press) and 32 switches (relays) to control my house. It uses HA autodiscovery. Everything works as I want - I have 32 switches and 96 triggers in HA.
a) I would like to have optional value under my Arduino device in GUI of HA with time of “LONG PRESS” treshold and send this value to device when changed via MQTT. It should by value between 400 and 4000 ms.
b) I need to send actual DateTime to my device periodically via MQTT.
How can I configure it? Can I configure it automatically via HA MQTT discovery?