OK, ex-elder here.
Yes Xmas - not cuz it's Jesus birthday two and a half months late but because it's happy Saturnalia, pagan see? - will get you DF'd.
Timescale? As Talesin said.
The guideline "we" as in whenever the elders had a school or the CO would "clarify" the elder guidelines was 2 to 3 years of inactivity before you might get a "leave it in Jehovah's hands" if you aren't causing a stir in the congregation.
So my advice would be - don't put up lights, flashing Santa or a fir tree in your living room if you are living in an area where you were known as an active jw. Ever. Because someone will be "stumbled" of course.