At the beginning I used to launch strategies on a 1-second TF, but I gave up soon since it’s so unreliable to me!

As for slippage…. it depends on volatility, volumes and news, rather than on TF. If you trade from roughly 14:25 thru 15:00 (2:30 pm – 3pm CET) on NFP day, expect a large slippage, sometimes a huge one if news are really unexpected!