How long should Roundup be left on Canadian thistle before tilling?

Three (3) days is the length of time to leave Roundup on before tilling land upon which Canadian thistle grows.

Specifically, the herbicide in question contains the active ingredient glyphosate. Its most effective application is after the harvest or in the fall. It must be used before the first killing frost and while soil moisture levels are conducive to herbicide-intakes.