From the beginning of the day of 15th (sunrise) = 04-03 06:00 to
the last evening hour of the 21st = 04-10 05:59, right before a new day begins.
The 1st and 7th days are #HighShabbat days. No work like any other #Shabbat days.
Remember, a day (24-hour period) begins at sunrise or 06:00 (for easy reckoning), and ends until the next sunrise or 05:59 (for easy reckoning).
We observe the Feasts of YHWH because he commanded these, not because of rituals men told us to. It is fine if you stick to pure Torah instructions or if you want to add traditions, it is between you and The Most High. Just make sure you are not doing it as a ritual, otherwise, it is legalism. Do it because you want to obey The Most High. It was YHWH who commanded these, not men, and definitely not the Pharisees.
“These things will make sense to some, but not to others. I don't want passive followers. Those who are truly committed will peer deeply into it, looking for Truth.”