What is the validity date of the Multiple Entry Tourist Visa and how long does it take to process?

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.

Multiple entry TR visa is back?

Timing is everything because validity begins on the day it was issued, as noted by

@Brandon ***********

Because it's now an e-visa application the process is faster and less expensive. Mine was approved in 3 days by the Los Angeles consulate.

It's the date the visa is issued.

Most e-visas are taking 1-2 weeks from application to receipt.