You do not have to square your hips... but I do. I practice squared hips and open hip splits. I do standing splits and on my back splits. I use walls, poles, yoga straps and my body to stretch. I work it from each and every angle I can. I love flexibility training! I use DVDs, Veena's lessons, online tutorials, articles and books to practice and learn different stretches.
There is a general time of 30 seconds to 2 minutes that is considered apppropriate times for holding a stretch. Around 30 seconds is where receptor cells disengage and gains in flexibility can be made... or so I have read. t is an extremely subjective thing and influenced by a persons level of health, fitness and flexibility.
Some stretches I will hold for two minutes, froggie, back splits, pigeon. Standing splits I hold around 40 seconds. Pikes and straddles, a few minutes. I tune into my body and let it tell me what is right for me at that time. It might sound 'woo woo' but it works for me. When I first started I couldn't do a split. Now I am training oversplits. Our bodies are amazing and I am proud of what I have accomplished. It is difficult, it is uncomfortable, it takes time and patience!
Just remember to be careful, stretching can cause injury. You don't want to cause pain or even worse, damage. Stretching takes time, patience and consistency. Listen to your body and allow yourself whatever time you need to reach your goals.
When I first started I couldn't do a split. Now I am training oversplits. Our bodies are amazing and so adaptive!