There are several ways to get to the page where you will be linking a thing’s channels to items. The direct way is to click on the channel list in the page for the thing and expand the channel you wish to link an item to:
When you click
Add Link to Item you will get the linking dialog. Fill in the item info as appropriate, and down at the bottom you will see the list of default profiles available to you including timestamp profiles. Just select the profile you wish.