Looks like Snap is compatible with 3.5.3 -> https://moodle.org/plugins/pluginversions.php?plugin=theme_snap - but the version listed there is 3.5.2 so is 3.5.3 the version of Moodle or the next version of Snap?
If you're taking about course start / end dates, then there is a 99% chance the theme has nothing to do with this.
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