The Jargon File (version 4.4.7, 29 Dec 2003):

larval stage
 n.

    Describes a period of monomaniacal concentration on coding apparently
    passed through by all fledgling hackers. Common symptoms include the
    perpetration of more than one 36-hour hacking run in a given week;
    neglect of all other activities including usual basics like food, sleep,
    and personal hygiene; and a chronic case of advanced bleary-eye. Can last
    from 6 months to 2 years, the apparent median being around 18 months. A few
    so afflicted never resume a more ?normal? life, but the ordeal seems to be
    necessary to produce really wizardly (as opposed to merely competent)
    programmers. See also wannabee. A less protracted and intense version of
    larval stage (typically lasting about a month) may recur when one is
    learning a new OS or programming language.


The Free On-line Dictionary of Computing (30 December 2018):

larval stage

   Describes a period of monomaniacal concentration on coding
   apparently passed through by all fledgling hackers.  Common
   symptoms include the perpetration of more than one 36-hour
   hacking run in a given week; neglect of all other activities
   including usual basics like food, sleep, and personal hygiene;
   and a chronic case of advanced bleary-eye.  Can last from 6
   months to 2 years, the apparent median being around 18 months.
   A few so afflicted never resume a more "normal" life, but the
   ordeal seems to be necessary to produce really wizardly (as
   opposed to merely competent) programmers.  See also
   wannabee.  A less protracted and intense version of larval
   stage (typically lasting about a month) may recur when one is
   learning a new OS or programming language.

   [Jargon File]