laskern – I would suggest you look at the first word in the Possuk – “Vayetzei” Yitchok. It is my suggestion that the Bal Haturim is comparing it to Motzei and Motzoh that the Baal Haturim brings in his explanation. The Baal Haturim is commenting on the odd phrasing. The possuk could have just said Yitchok met Rivka. What is all this going out of the field after supplicating there and then he met his bride to be!
Although the Baal Haturim does not say that mincha is a most beneficial time to daven for a shidduch, I think there is a smattering of that in his explanation. Also although the Shidduch had been worked out some time before that Mincha prayer – Yitchok didn’t know that!