Formal:
* À quelle heure le vendredi? (This is the most literal translation and the most formal)
Informal:
* Vendredi, à quelle heure? (This is more natural in spoken French)
* Quel heure, vendredi? (This is very informal and might not be appropriate in all situations)
Example sentences:
* "À quelle heure le vendredi vous voulez-vous rencontrer?" (At what time on Friday would you like to meet?)
* "Vendredi, à quelle heure est-ce que le film commence?" (What time does the movie start on Friday?)
* "Quel heure, vendredi, tu peux venir?" (What time can you come on Friday?)
Remember that the specific way you say it will depend on the context and the level of formality you want to achieve.