This isn't something there's a definitive answer to; not everyone gets premenstrual symptoms before each period, and people who do won't necessarily find that they start at the same time each cycle. So, you really can't assume anyone's period start date based on when PMS symptoms might appear.
People who chart their cycles and make notes about PMS symptoms might, over time, notice patterns they can use to estimate this for themselves, but that data will be unique to them and not applicable to other people who menstruate.
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