The 3-Day Challenge (also called 6-Day Challenge) is pretty hard. You have to have skill in order to beat it. As well as know all the dungeon shortcuts: what to get and what to skip. I've done the challenge plenty of times, so here's my personal advice. Before you start the challenge, take a few days to go through each dungeon and take notes on what to do. For example, take a look at the Woodfall Temple map below. There are already two rooms you can skip: the Compass and Map rooms.
Also, you don't need to get all the Small Keys in a dungeon. Just the Small Keys that let you progress without all the additional items. The only items you need to get in each dungeon is the Boss Key and the dungeon item. Just do that to each dungeon.
After that, plan your route. Find out what happens on what day. In Lamentizer's guide, you need to get the first two temples complete, get the powder keg, and rescue epona all before the first night, because that's when the aliens come to attack the ranch. And don't walk!!! Roll or spin!!! Using the Deku Mask saves lots of time. When you get the Goron Mask, roll everywhere. In the dungeons, switch between the Deku and Goron Masks. Remember don't walk but spin\roll. Even if you're three feet from the door, spin or roll. You will save so much time. If you make a mistake, you're screwed.
One last thing: practice. Take the challenge slowly. If you fail to get epona by the first day, start the cycle over again (power switch or RESET) and keep going until you make it. If you get Snowhead done by 9:00 PM, try again. Next time it might be 7:00 PM. And then 6:30 PM.
But, I wish you the best of luck. If you have any other questions feel free to ask me.