I will be on leave starting on October 4th till October 5th
I will be on leave on October 4th and 5th
I am on leave from October 4th till October 5th
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Sign up to join this communityI will be on leave starting on October 4th till October 5th
I will be on leave on October 4th and 5th
I am on leave from October 4th till October 5th
Your second option most clearly states when you'll be on leave. Saying "till" doesn't make it clear if you're returning the morning of the 5th, or if the 5th is included in your leave.
To be absolutely clear, you should state when you leave and when you return.
I will be on leave October 4th and 5th, and I will return October 6th.
This makes it clear which days you will not be in the office.