though i cant solve all your question at once, but i can give you some guidelines untill a more experienced person comes through,
to assign variables in linux use the comand as follows
example
set variable="as"
then to call on it use $variable
variable being any name you want.
as for using mathemtical numbers it would be the same thing unless you need arithmetics for them you can use the "expr"
to read variables a user inputs , you would define a varialbe then use the read command
example:
#!/bin/bsh/
echo " please enter what time u would like shutdown"
read TIME
echo $TIME
this should cover the ruff idea ill try and get back to u if i go through more,
p.s. for date & time option the command is date , Try man date to see more options, i dont know much of the top of my head
Good Luck
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