The phrase "chunk of time" typically means a period of time that is significant or sizable enough to allow for a particular activity or task to be completed. The duration of a "chunk of time" can vary depending on the context, but it usually refers to a block of time that is more than just a few minutes or moments. Here are some examples of how you could use the phrase in a sentence: "I need a chunk of time to finish writing this report." "Let's schedule a chunk of time for us to discuss this project in more detail." "I can't do this task in just a few minutes, I need a bigger chunk of time to complete it." Other ways you could express the same idea include "a significant amount of time," "a sizable block of time," or simply "a period of time."

I agree with what Ahmadi said, and I would just add that in simple words here a "chunk" means an amount of time that is not insignificant. Relative to whatever scale is appropriate in the conversation, a "chunk of time" is not so small that it can be ignored.