B2 visa stay extension - less than 15 days for i94 valid date

[newacct]

Is it mandatory to apply for extension 45 days before end of current stay period? Reading the instructions document, I felt that it is just a suggestion. Below are the exact words from the instructions document that I downloaded from the USCIS website. Would like to hear what others have to say about the timing of application of extension.
"Therefore, we suggest you file at least 45 days before your stay expires or as soon as you determine your need to change or extend status."

It's just a suggestion. It just needs to be received before, or on, the day your status expires.