So, the complete sentence is: "The meeting is scheduled at 1:30 pm."

The preposition "at" is used to specify a particular point in time, like an exact hour on the clock. In the sentence, "The meeting is scheduled at 1:30 pm," the phrase "1:30 pm" represents a specific, precise time, and that's why "at" is the correct preposition to use.

When we talk about scheduled events or appointments, we often use "at" to indicate the exact time when something is planned to occur. It helps in pinpointing the specific hour or moment when the meeting is set to begin, in this case, at 1:30 pm.