Even if the dialogue that follows that sentence is:It should mean that the coffee has been sitting on a burner for 48 hours. This coffee would be bitter and practically undrinkable to people who really like coffee.
"Blend" is a normal term for blended coffee. In your example, "48-hour blend" is a joke.
They are being ironic, fexga. If this is the coffee that somebody made in a police station or an FBI office, the chances of it being undrinkable are very high. Typically, somebody makes a pot of coffee in the morning. It sits on the burner for hours and turns into a sour, black mess.(guy who made de coffee)-That's right. That's the best coffee you're gonna get anywhere.
(another FBI aget) -We sure need a good wake-me-up, right, agente Desmond?