Needing help with random ticking for an infection mod

So I've been developing an infection mod recently and I've gotten stuck.

So at the moment my mod adds a block that will replace surrounding blocks with itself, slowly spreading across the entire world. The block originally used randomTickSpeed to spread itself, meaning that if you wanted to increase the rate of infection you would also need to increase the rate of everything else that uses randomTickSpeed. Because of this, I tried making my own gamerule what would function similarly to randomTickSpeed but it would only affect my block's infection rate. I have been trying this for two hours as of right now and I have made little progress. Can someone help me to make a custom gamerule that achieves the same effect as randomTickSpeed but works exclusively for this block?