How long can my lightning node be safely offline? I am interested in setting up a full bitcoin and lightning node on my pi.  I want to open a few channels and be well connected in the network.  I intend to keep this machine on permanently, but may have to unplug it if I need to move it to a different socket or maintain it.  How long can my node safely be off the bitcoin network without risking loss of funds in my channels?
that depends on the locktime that is configured for your channels. taken from c lightning (c.f.: https://github.com/ElementsProject/lightning/blob/97118c558e84e0b3a12a8cbe60528ad5cfcb2fd6/doc/lightningd-config.5.txt )


  watchtime-blocks='BLOCKS'::
      How long we need to spot an outdated close attempt: on opening a channel
      we tell our peer that this is how long they'll have to wait if they perform
      a unilateral close.
  
  max-locktime-blocks='BLOCKS'::
      The longest our funds can be delayed (ie. the longest watchtime-blocks
      our peer can ask for, and also the longest HTLC timeout we will accept).
      If our peer asks for longer, we'll refuse to create a channel, and if an
      HTLC asks for longer, we'll refuse it.


I believe the standard setting should be 144 blocks which statistically should be 24 hours. of course you should consider a safety window to be able to get your breach remedy tx mined in case of a unilateral close.