Would it sound awkward if I say "expansion" instead of "extension" in this context?

Native speaker’s answer
Rebecca
Yes, it would sound awkward if changed from "extension" to "expansion!" This is because, here, "extension" refers to the length of time. They're talking about the length of the contract in terms of time. "Expansion," while it could refer to length, is more about the "largeness" of something - something becomes bigger. <Time> cannot "expand", but it can "extend" into the future. Ex: The balloon expanded when she blew it up. Ex: They're expanding their business. Ex: They're adding an extension onto the house next door. Ex: The caves extend for about 12km. => length Ex: My teacher gave us an extension for our project deadline. => length of time