I only post to give some background info. My wife has an on-line bank account. Whenever she is online and wishes to transfer money to somewhere else - at some point in the transaction she has a to click a button on her PC and almost instantly her mobile phone 'dings' as it receives a text with a secure code from the internet bank that she then has to input to the PC in order to proceed.
There is virtually no delay between her clicking the button on the PC and the text being received. I don't know if there is a time limit for the code to be entered into the PC, but if there is it has never been an issue. Hope this helps in some way.