NTD:

As I read the rules -- and looking back at old statements, this seems to track experience -- when you trip the threshold for Silver or Gold, you are a) instantly changed to the higher level; and b) your annual re-qualification clock is reset to the end of the "new" month.

Same with PPS. However, once at PPS, your annual re-qual month will remain the same so long as you continue to maintain that status. It has to: there's no higher annual earning level to reach (Solitaire is just 5 consecutive years of PPS)