Make sure you checkout the Immigration DTV extension documentation requirements first, they appear to be possibly more demanding than the MFA initial visa requirements.
Are you sure its not "eg: TM30", which is a possible existing document if you are already residing in Thailand and have had to leave purely to obtain a new visa and returning to same address within the check-in period.
As James said, you must go on the date given, as this will be the date it is issued and comes into force, if you go on later date there would be a gap between expiry of consideration period and day you go in where you have no permission to stay, so would be on an overstay & apart from the fine they may refuse to issue a visa extension.
It all depends on volume of notifications, i've had to wait over a week before now, and sometimes its been back within 24 hrs. Just wait until 30th and if its still pending (on the web site) you still have 7 days to visit CW and do it in person. Check your spam/junk mail folders for notifications in the meantime.
correct if your only remitting your social security or armed forces pensions, can't recall the private pension entry. Other remittence may be subject to tax depending on source and when realised.