You can extend the roll to about 5 hours max. Redosing increases the likelihood of harm and after 5 hours you will no longer have the same kind of high.
Smoke some weed or take GHB to extend the fun for a couple of hours.
What's the practical difference between taking 200mg at once and taking 100mg twice 30-60 minutes apart? A longer but weaker roll? Better afterglow?