If you had an ATS, then you would have tested it...
It depends on the system, though...
If it's an outright intraday swing model, then I would generally include it. If it's an scalping or a pairs/arb type model using Tick to Bid/Ask data then I wouldn't.
The trading style of the model, timeframe, product... and etc..... there is no right answer but to test, test, and more test.