Easyflexibility

The only way to get it in one day is to force it, and risk seriously injuring yourself. And then it may take longer to recover than it would have to get the splits normally i.e. through gradual stretching. Forcing it means you or someone physically forces your legs apart despite the pain.

The best thing to do is take one beginning yoga class so that you know how to properly stretch without hurting yourself. Do those beginning poses a little more each day for a couple of weeks. Be gentle with yourself and never in a rush. All poses have variations. Shoot for the simple variation until you can comfortably do the more difficult variation.
Try to keep a daily schedule. When you get out of bed do one simple stretch, it could be a forward bend, try to reach the floor more each day. If you already can do that, go further, hands wrapped around ankles. Or do a torso twist to wake your body up.

Stretch all over one day, stretch just lower body one day. Increase your awareness of your posture during the day. If you find yourself seated on your lower legs again, just uncurl and stretch a little bit. Breathe slowly and hold your stretches for the same amount of breaths each session. If you keep it up you'll likely be able to do a split soon. Listen to your body, if there is any pain or discomfort, don't continue.
Difficulties in yoga asanas come differently for each individual, depending on their body and your experience with those asanas. Some people have more strength and are more comfortable with arm balancing asanas (grasshopper, firefly, peacock pose), whereas more flexible people are better at backbends (wheel pose, camel, or happy dancer pose) and inversions (plow pose, shoulder stand).

For me personally, I’m quite comfortable with all these as I started practicing yoga at a teenage age, so I’ve already acquired the strength, flexibility and endurance in yoga. But I still have a lot to work on for arm balancing poses. I’ve only recently managed to hold in grasshopper pose for long enough, but still need to work more on the advanced arm balance pose. The other day, I was attending one advanced yoga class; as we came into one legged wheel pose, no one in the class was able to pull that asana except for me. Even the teacher said he envied me as he still couldn’t pull the perfect one legged wheel pose. I didn’t want to show off by telling him I’m also a certified yoga instructor.

how to do the splits in one day

Nevertheless, as you advanced with your yoga journey, even your strengths can become your weaknesses - you’ll always find things that will challenge you.

https://www.easyflexibility.com/blogs/flexibility-pearls/how-often-and-how-long-to-stretch