For at least 3 months means each and every day of those 3 months.
If they wanted to see the last day of last month they would ask for the last day of the last month at 16:59 hours, just before closing time of the bank.
Each and every application is reviewed on its own.
What ever dozens of anonymous experts are going to tell you, you can NOT use their anonymous DTV as proof that the Embassy where you applied MUST give you a DTV.
If you can not meet the requirements, keep working until you can and apply when you meet them all.