Test and tune events are just that. You get as many runs as you want so you can test your car, tune it between runs (if you desire) and test again. How many runs you get depends on how early you get there, how many people show up and how many oildowns there are. If you get there by 10am you should easily be able to get in 10 run if not more.
Atco is a great track. It about 100' above sea level and it should be nice and cold on the 21st.