For a realtime trend view, you can have 900 (or is it 999 ?) values to display.
So for 8 hours, the cycle trigger must be set to (3600 sec/h x 8 h) / 900 = 32 sec.
If you want to look further back in time, the cycle trigger must be increased accordingly.
I do this, by having several trend views for the same variables for 1 h and 4 h respectively.
That said, for trending values far back in time you really need to use archived tag values. It costs an archives license.