It is a fused sentence (Some times called a run-on sentence). See possible corrections below.
The parade to support the veterans begins at noon on Saturday;
be sure to arrive an hour early.
The parade to support the veterans begins at noon on Saturday. Be sure to arrive an hour early.
I think (tbh not sure) but the best would be "The parade to support the veterans begins at noon on Saturday,be sure to arrive an hour early" or "The parade to support the veterans begin at noon on Saturday. Be sure to arrive an hour early"
