Suppositional sentences having phrases like “I wish”, He/She wishes”, As if”, As though”, and indicating some unfulfilled wish/desire take simple past.
They are late every time
the singular “they” is a generic third-person pronoun
and with a singular noun only the plural form of the Verb is attached that's why "are" will be the correct word used in the sentence
If it is plural or there is more than one noun (they), use are.
ND7-3-2023