Is there any standard/recommended design pattern for verifying phone numbers using One Time Pass-code (OTP)?

Is there any standard design practice/pattern for mobile phone verification using One Time Pass-code (OTP) ?

Practical efforts to understand existing systems indicate that most of them use similar design.
( Oddly enough, I've not been able to find any such standards specifying the same )

Just to mention a few cases

1. Is there any standard specifying the exponential/sequential increase in time delay for handling resend requests ?
2. What is the recommended expiry time for a newly generated OTPs ?