New Presidents make their first 100 days in office a benchmark for success, pledging to enact headline policies quickly. It started with FDR whose bold plans for change meant his term began with a three month special session to pass laws designed to help turn around effects of the great depression.
JFK played down the significance of what could be done in 100 days, claiming that some things might never be accomplished but it's important is that we start.
I can't see that point of view being widely accepted in today's world of short attention spans and tribalism. Fast gratification over long term improvement is what gets people on side.
JFK also promised men on the moon by the end of the decade at a time when no one at NASA knew how to actually achieve it, pushing them to figure it out. There can be a benefit to limited time to make progress, but if it backfires someone ends up looking bad.