Visa is currently forming an uptrending channel, a trading range that's bounded by a trendline resistance and trendline support level. Those support and resistance levels give us a high probability range for V to trade within. And as you might expect, the ideal time to be a buyer is on a bounce off of support.
When you're looking to buy a stock within a trend channel, buying after a bounce off of support makes sense for two big reasons: It's the spot where shares have the furthest to move up before they hit resistance, and it's the spot where the risk is the least (because shares have the least room to move lower before you know you're wrong). Visa is testing trend line support this morning, but a move higher looks likely from here -- there's considerable demand along that trend line. I'd look to build a position if strength stays in the market by this afternoon.