Wave spawner and word length

I’m trying to create a falling word typing game like z-type.

I have used the code provided here : https://github.com/Brackeys/Falling-Words-Typing-Game

In the WordSpawner.cs file, I’m trying to set the limit of the length of words that are displayed. for eg. in the first 15 seconds I want the length of words to be 3/4 and between 15-30 seconds 5/6 and after that any random length from 3 – 9. Is there any way to achieve this?

Also, I want to show the wave number on the screen like in the z-type game. How can I achieve this functionality.