Just do yourself a favor and include one more week.

It doesn't matter what kind of project, always include one more week.

Don't be upset if you can't stick to your plan, allow yourself an extra week.

It's not your fault, that's basically software engineerings nature.

You should get out daily, for at least 1 hour. Simply because that one hour is for recharging your brain, which again leads to better performance.

Also what I try to do, when I'm doing a hackathon, is that I'm looking for templates from themeforest or wrapbootstrap.

There are also a lot of good templates for your framework, where auth/register/signup/signin/roles etc. is already done for you.

I don't like reinventing the wheel, I'd rather focus on the business logic.