If they're not specific about which letters to use, we can use p, q, and r.
so p is "i will get up on time"
q is "the alarm goes off"
and r is "the alarm is set" (i guess it could also be "the alarm is not set" but it's more common to write a statement with the "not" and let a negation put that in for you.
"if and only if" is the double arrow (biconditional), "or" is the V shape (disjunction)
so translating each piece we have:
(p <--> q) V ~r
the placement of a comma like that usually means that the or should take place after the biconditional is done, and shouldn't be part of it like p <--> (q V ~r)