Not at all. You can start at any point. EASY simply helps give some structure to our day, and helps us to understand our LOs better. Could you post the routine of the entire day, please?
A few points --
At 5 months, A times increase and are closer to 2.5 hours. Since you are getting short naps anyway, you could gradually add 10-15 minutes and then hold at that point to let her body adjust - then add again. If it is possible for you to darken her room more - blackout blinds/double curtains - it definitely helps. So our nap time routine was - walk around a while before hand to calm her down talking/singing/humming, then go into a dim room and put her in her sleep sack/swaddle, then sing sleepy song, lay her down in her bed, turn on music box, turn off light & leave the room. You can start by using the 4S wind down routine and then incorporating elements of your own into it. It would take her a few days to catch on and she might protest the change but she will understand soon enough. It helps to keep a log of your day:)