@Mike *******
, the requirements of the remaining days are totally different for applications for in-country visas and extensions. As a general rule (means at most offices),
For in-country visa applications, you have to have MINIMUM 15 days (means when you have 15 days or MORE remaining) with your current entry stamp to be able to apply for an in-country visa. Because the "under review" period is before the visa is granted.
For a 1-year extension application, you can apply when you have 30 days as MAXIMUM remaining (means when you have 30 days or LESS remaining) with your current stamp after you get an initial 90 days stamp. The "under-consideration" period for some type of extension is the first part of a new extension after the extension is granted, and that would be added.
(the last day you can apply for a 1-year extension is the date on your current stamp).