A Non O e-Visa, in UK should take approx 4 days.
When the Visa is issued it has a "validity date" It is valid from date of issue for 90 days.
You need to enter Thailand while the visa is valid.
When you enter Thailand they will give you a 90 day stamp.
Understand that at that point you no longer have a visa.
You have a permission of stay (permit)
After you have had funds in bank for two months you can apply for 12 month extension of your permission of stay.
You can to that up to 30 days prior to expiry. 45 at some offices such as CW, CM etc.