The date on the visa is the date that it's valid from. All Thai visas are valid from the day they're issued, Thailand will not post-date a visa so you should apply for it as close to your entry day as possible.
Also note, while the METV is valid for 6 months, each time you enter Thailand you'll only be stamped in for 60 days. If you enter on the last day the visa is valid for, you'll also he stamped in for 60 days, with an in country extension you can get roughly 9 months from a METV.