No need to worry... some times ours emotional status can shift menses dates... 5 days fluctuation is normal

You don't need any remedy for this. It's common. Reasons 1 travel 2 change of weather 3 change of place 4 if you have drunk too much juice 5 stress It might not repeat the same way in the next cycle. You might get your cycles on 28th day too. If you are planning pregnancy then make sure you copulate from 10th day to 20th day of your cycle either everyday or once in 2 days. If you are not planning then wait for another 2 cycles to understand if there are any changes

Few days overdue is normal if menstrual flow is normal without clots and abdominal cramps. Delayed  periods with heavy flow and pain then consult.

21 to 35 days gap is ok. So no need to worry. If further delay occurs may need some life style changes

If your dates are postponed for 4 days then day of ovulation also may postponed. If you are planning to conceive then kits are available in the market with which you can check day of ovulation at home by yourself. Thank you