Kinda depends on how big a change it is, and what numbers you'll be going thru on the way. If you hit 77, 76 or 75 then your code as displayed on the tube starts flashing, alarms start beeping and the D&D cell at LATCC start getting excited.
If it's only a quick change (as others have said, no more than 4 or 5 secs) I wouldn't worry too much!
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Once more unto the breach, Dear Friends...