What I do is this:
(1) Fire up a listen server with just me in it
(2) Pull down the console by pressing ~ or `
(3) Type in demorec name for the demo - eg. demorec test
(4) Whizz around the map, doing whatever you want
(5) When done, type stopdemo in the console.
(6) Return to the main menu.
(7) To play back the demo as a timedemo, type in the following: demoplay name of demo?timedemo - for example, demoplay test?timedemo.
(8 ) Once the timedemo has finished, it'll return to the main menu again and if you pull down the console, the number of frames, length of time and average frame rate will be displayed. You can record and timedemo botmatches in the same way if you wish.
I've found that UMark doesn't work with my install of UT2004 for some reason.