Yes, as often as you like. The demo carries no cap on attempts, and each one is a new session rather than a continuation of the last.
Nothing survives from the previous sitting — not the clock, not the answers you gave, and not the arrangement the items came in. What a retake changes is the arrangement rather than the material, and that is still worth something to somebody preparing for a networking certification exam.
What Changes When You Sit the Demo Again
The sequence the items reach you in is set again, and so is the order of the options underneath each one, so the position an answer occupied last time carries no information this time. What a retake does not promise is unfamiliar material. A demo is a short sample by design, and a second attempt may well put the same set in front of you in a different arrangement rather than a fresh one — which is exactly why the arrangement is the part that moves. Because a demo attempt cannot be paused, leaving one part-way through is not a suspension either.