How to put a date token at the start of Backup and Migrate file name pattems?
On the Advanced Backup options page below the Backup filename there is a link Replacement patterns which expands to display another link Current date which displays some of the tokens available. None of the existing ones suits my preference which is a numeric date.

Using the PHP date options a good date prefix would be [current-date:custom:Ymd-Gi] or [current-date:custom:Y-m-d-Gi] the latter resulting in a string like '2013-11-17-1924' for 17th November 7:24 pm.

As an example I have a Backup filename token [current-date:custom:Ymd-Gi]_[site:name]-PMU, the PMU meaning Pre Module Update, something to use just before upgrading modules so you can revert the configuration if something goes wrong