Sign up for an account on the English Nico Nico site
. You can use the same login for the JP site, so after you're done registering, log in on the JP site.
To timeshift a program, click on the yellow button with the clock on it that says "タイムシフト予約" (Reserve Timeshift) on the program page or the Nico Nico Live page
. A popup will appear saying that the timeshifted program will be available for viewing 30 minutes after its broadcast. Click the yellow button again to reserve the timeshift. The popup will change to one saying that the timeshift has been reserved and that you can set notifications before the program start be sent to your cellphone. After you've reserved the timeshift, the yellow "Reserve Timeshift" button will be grayed out.
To see your list of timeshifts, hover over "メニュー" (Menu) on the upper right hand corner of the top navigation bar and go to "マイページ" (My Page) on the dropdown menu. With a free account, you have 10 timeshift slots. If you use up all ten, you will need to delete a program to clear up a slot. You can do so by clicking on the red "[削除]" (Delete). To watch a timeshifted program, click on the red button with a clock on it that says "視聴する" (Watch). Viewing rights for timeshifted programs differs from program to program, so always check if there is a date and time (in red) by which you can watch a timeshift before it expires. For most timeshifts, once you start watching the program, you are given about 24 hours until your viewing rights expire. So if you start watching something, you should finish watching it as soon as possible.