Well, first off, no the 5D does not have a built-in "intervalometer" -- in fact I'm not aware of any Canon DSLRs that do (although maybe some of the newer ones, but I haven't heard of any).
So, I believe the Canon EOS Utilities can do this -- it does "tethered" shooting and I do believe it has an intervalometer function but I've just never looked at it.
The Utilities came on the disk that comes with our DSLRs. If you don't have the disk(s) then you'll have to speak up -- there are workarounds. You can start with checking this site:
http://www.northlight-images.co.uk …stall_canon_software.html
Now, I'm not a Mac user so I don't know about how they handle things. With the older 5DC there have been issues with lack of driver support for the 5D in Windows and people have had to jump through some hoops and I'm not sure of the current state of things -- I have my 5D but have never actually used it with EOS utilities (or any other reason for connecting it to my computer).
So, install the software and try it out. You will need to look into either Help or the manual/User Guide -- it's on the second disk but if you don't have it you can get it online through the Canon site. You can also download an upgrade to the Utilities and the other Canon software.
Aside from buying new software for this, the only other way I know of is to have a remote that has intervalometer capabilities. My Canon TC-80N3 cable shutter release has this (using a little battery) and that should work fine for this as long as the battery holds up. But, that's a piece of hardware, and I don't know how easy it would be to track down. Phone calls to camera shops could help.
Another question would be the power supply for the camera -- having at least one fully-charged spare on hand would be very, very important, unless you have an AC adapter for the 5D!