At least one, very popular, video on changing the timing belt has the procedure for tensioning the belt completely wrong.
Use the proper timing marks and procedure from the workshop manual that I linked to above:
The point is that the tensioner is not set at TDC, but at 1/6 turn on the crank before the cam timing marks align (so 1 and 5/6 turns on the crank forward from when the marks are aligned) - Mazda even put a mark on the casting to show the correct position:
Personally, I don’t think it matters too much whether the tensioner is tight or loose when you first turn the engine over [by hand], as long as you stop in the right place to set it finally. There’s less chance of the belt skipping while you turn it over if the tensioner is done up.