With the sunscreen you will probably get close to nothing. I am very fair, I burn in 20 minutes in the hot summer sun, and if I use just 8 SPF I get nothing—I stay white. Unless, it’s many many hours out in the sun, and maybe that’s because it’s fading off of my skin after many hours. With spf 15 and higher I get nothing period. I can walk around Disney for 10 hours and the 15 completely protects me.
I haven’t done it in a long time, but I used to get tan by going in the sun for 15–20 minutes and then putting on my sunscreen, or flipping over to my other side if I’m just laying in the sun, and doing that 4–7 times in a week.
You will get a feel for how long you need. If you stay out 20 minutes and seem to get nothing, you can increase it to 25, etc. You might want to start at 15. The tanner you are, you will be able to stay out a little longer, but probably not much since you are very fair.
This time of year, winter, the UV index and the power of the sun is lower, so it’s not a bad time to test it out, but beware, the cooler air is deceptive. You might feel like you are not getting any sun, but trust me you are, use a timer.