In a normal working set 5 minutes is usually ok. However if the set has problems in the HV or focus divider circuitry a week may not be enough. I always try to measure it with a HV probe to make sure, I got bit once and never again!
I always use isopropyl alcohol and allow plenty of time for it to dry, then if needed use an electrostatic plastic spray on the tube around the HV connection. Most projectors now days use sealed connections at the CRT for the HV connection so don't mess with these.
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