When is a reasonable amount of time for patients to be on 90 mg BID of ticagrelor before transitioning to 60 mg BID following PCI?  

That depends on the type of PCI. Generally speaking, I do not continue Ticagrelor beyond six months for stable angina PCI and one year for PCI in the setting of acute coronary syndrome. If the patient has had recurrent ACS or complex bifurcation PCI, I would transition them to 60 mg BID after one ...