Альтернативы gnome-clocks

at 20:00 tommorow

At  allows  fairly  complex time specifications, extending the POSIX.2 standard.  It accepts times of the
       form HH:MM to run a job at a specific time of day.  (If that time is already past, the next  day  is  as‐
       sumed.)   You  may  also specify midnight, noon, or teatime (4pm) and you can have a time-of-day suffixed
       with AM or PM for running in the morning or the evening.  You can also say what day the job will be  run,
       by  giving  a  date  in  the  form  month-name  day  with  an optional year, or giving a date of the form
       MMDD[CC]YY, MM/DD/[CC]YY, DD.MM.[CC]YY or [CC]YY-MM-DD.  The specification of  a  date  must  follow  the
       specification  of  the time of day.  You can also give times like now + count time-units, where the time-
       units can be minutes, hours, days, or weeks and you can tell at to run the job  today  by  suffixing  the
       time with today and to run the job tomorrow by suffixing the time with tomorrow.

       For  example,  to  run  a  job  at 4pm three days from now, you would do at 4pm + 3 days, to run a job at
       10:00am on July 31, you would do at 10am Jul 31 and to run a job at 1am tomorrow, you would do at 1am to‐
       morrow.

       If  you specify a job to absolutely run at a specific time and date in the past, the job will run as soon
       as possible.  For example, if it is 8pm and you do a at 6pm today, it will run more likely at 8:05pm.