a client wants me to develop a game for web&android&iOS.
This will be the first time I upload something to the Apple Store and would like to have an idea on how many hours I may need to get the C3 creation ready for iOS and properly upload it to the Apple Store, as well as any other thing I should take into account.
Also, as I don't have a Mac: should I just subcontract someone to do this process?
Develop games in your browser. Powerful, performant & highly capable.
The time needed depend of the complexity of your app.
If it's not a game and so you don't need to implement IAP, ads and GameCenter it's quick enough, but you have to support all screen sizes of iPad and iPhones.
You need to allow time for registration with Apple, the cost of it, the time to register your app too etc.
You need a Mac, or you can rent one online.