What are my options here?

I've used SQL-DMO for job related stuff before in VBScript, but for finding out how long a job took to execute (in minutes for instance) I'm stumped on.

the stored proc sp_help_job is great for finding out the date and time a job started on, but not when it finished - only the execution status (did it succeed or not?).

I need to get output using VBScript (or Visual Basic I can convert to VBScript) that will say

SQL Job xxx took 25mins 11secs to run (or something to that effect).

I'm writing a vbscript to monitor whether a certain job takes longer than 20 seconds to run on a number of servers.

Any thoughts? I know SQL-DMO is probably the way to go - but I'm not sure what I should be invoking to find out the information I want.