Devices> TV> Settings> Adjust Power Settings is - reasonably enough! - the place to look for the power-on delay.
That deals with the problem if it arises only when turning on the TV. If it happens when changing from one Activity to another you need to look at the way you set the inputs. With a Toshiba that should be method 2 even though the software says otherwise. You should be using that anyway so it's worth changing if it's currently different.