I cannot find any hooks in the style templates under memberslist!

However, I created a new plugin and guessed that "memberlist_complete" would be the correct location.

How would I go about changing the date format of the Last Visit then? I tried the following;

How do you know what to put inside the ['....']? At the moment Im just kind of guessing at the names, is there a dictionary of vbulletin terms available anywhere?

Look at the member.php page. That is where I am saying to look for the hooks, not in the templates.

At the top is the member_start hook. Simply set the *option* to what you want. ie.
(Or whatever option you want to change.)

Thanks for the reply.

memberlist_bit seemed to be the hook that in fact effects the date format.

Sorry if this is a silly question, but what should I put for the $timestamp part?

What I'm saying is.... just change the option. If you look at the vboptions page, and find where dateformat is defined, you'll see the options in the page source. For instance, if you wanted to change the Yesterday/Today option, find the option in the vBulletin Options page and look at the page source:
I highlighted the allowed values - 0, 1, or 2. If you wanted the date to use Yesterday/Today on that page, that would mean you want the value set to 1. So, you would put this in the plugin:

All done. Many thanks for your help and patience :)