clock calibration 

simply use the code from the set sketch that grabs time from the computer (assuming that you don't need to run IDE to use this) 

either have it run on startup to check if the answer isn't null and if it isn't, set (some sort of try catch for that) 

or have a button that you hold to go into 'clock setting' mode 

in the manual - if the day is wrong, you can do that but keep in mind the drift of when a day starts - ie 12am, 2am, 3am, etc. 

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have a switch you can switch, then a website 
you turn on the switch before turning on the module 
then connect a eurorack cable to your computer 
the site communicates the current time over serial 
or just over a series of blips that communicate the time 

could do something simple like giving year, date, hour
each one expressed as a series of short blips, with a long one in between

real easiest is prob setting up a long var that is seconds since 2000 as a binary number 
then the thing communicates binary - maybe with a long pulse in between
In calibration mode an LED lights up when its calibrated

Note - this setup would also forgoe the need for a USB port, so things could be SMD

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