Is there a way to check if an entity is on/inside a specific block?

Hello there! I am currently working on a Frozen Zombie in my Minecraft mod, and I was just curious if there was any way to make an entity transform into another if it was on a specific block for a long period of time, similar to when a Skeleton transforms into a Stray if it is in powder snow. For instance, I was aiming to make Zombies transform into this new type of Zombie if it was in/on a block such as powder snow for about 30 seconds. Thank you for your help; have a great day!