Hi Niwantha, You left a message "for" Ann. We use the preposition "for" and not "to" here because there is a meaning of purpose or doing someone a favour. You left a message for the purpose of informing your boss. Example: I am bringing the package to you. ("to" expresses a movement and a recipient) I am bringing the package for you. ("for" expresses doing someone a favour.) I would modify your first sentence: "I am on a half day leave." or "I will be on a half day leave." "Leave" is needed for your absence from work and makes your sentence complete. I hope this helps.

for my boss a half day

""I am going on a half day." This sentence is an incomplete thought. Where are you going on a half day? If you say, "I am going on a half day trip to the seaside."" then it is correct. Or ""I am going on half day leave from the office/work." then it is correct.

"for Ann” and “a half day