Complete the tired student's dramatic reply.

Barista: "How long have you been studying?" Student: "I have been awake _____ Tuesday morning. I think I forgot how to sleep."

The correct answer is since.

When answering a "How long have you..." question, we use since followed by a specific starting point in time (like "Tuesday morning", "2015", or "last week"). We use for when talking about a duration or length of time (like "three days").