Please wait for another 5 minutes
Or
Please wait another 5 minutes
Isn't "for" mandatory because 5 minutes is length of time?
Please wait for another 5 minutes
Or
Please wait another 5 minutes
Isn't "for" mandatory because 5 minutes is length of time?
Isn't for mandatory because 5 minutes is length of time?
No.
In "Please wait another 5 minutes", "another 5 minutes" is a noun phrase acting as an adverb (or to be more precise, as an adverbial prepositional phrase) to modify verbs and certain adjectives.
They produce a complement.
These constructions are known as adverbial objectives and they are common with time and distance phrases.
The Free Dictionary has examples:
Time
“I am leaving tomorrow.” (originally = on the morrow = in the morning)
“We walked [for] an hour out of town.”
“I’ll see you [in [the]] next year.”
Distance
“I run [for] five miles every day.”
“I can barely see [for] a foot in front of me in this fog.”