Can i say, Jeg er her alle tiden?
You can say "Jeg er her til alle (døgnets) tider", but "hele tiden" is much more common.
can I say, jeg er her den hele tiden?
No, "hele" and "halve" do not take "den/det"; they're the exceptions to the rule.
Is hele tiden used to mean often or literally all the time?
all the time
Colloquially, I thought this sentence could also mean 'I am going to be here the whole time.' If that is not correct, how would you express that sentiment?
Probably "jeg skal være her"
"Jeg blir her hele tiden" is one option.
... på skolen :c
Ikke jeg lenger. Hehe.