We'll have a five-day holiday in China, from tomorrow to May 5th.

🥲

ItThis week has been a little busy this week, but I can feel theit busy for me, but I felt relaxationed after today's lunchtime.

The May Day Holiday is Coming!

We usually add “the” with “holiday.”
For example:
Christmas is coming.
The Christmas holiday is coming.

We'll have a five-day holiday in China, from tomorrow to (suggestion: through) May 5th.

“To” is ambiguous as we can’t tell whether the 5th is the last day of the holiday or the first day back at work. “Through” makes it clear that the holiday includes the 5th.

It has been a little busy this week, but I can feel the relaxation after today'smood in the office has relaxed since lunchtime.

Present tense seems fine to me if you’re writing this in the afternoon, after lunch.

“Today’s lunchtime” doesn’t sound idiomatic to me. “Today” is implied in my correction.

I will go hiking tomorrow and the day after (tomorrow).

The second “tomorrow” is unnecessary.

Alternative: I will go hiking tomorrow and the next day.

But we also need to be careful because venomous snakes {have also begun to become active | are also becoming active}.

“Begun to become” is grammatically correct but sounds a bit awkward.

I'm also looking forward to this holiday now.

This sentence sounds unnatural, as if you weren’t looking forward to the holiday before this moment (which clearly isn’t true). “Looking forward” doesn’t convey the eager anticipation of “期待” in this context. I would suggest: I can’t wait for this holiday to start!

I will go hiking tomorrow and also the day after tomorrow.

what you have is correct but you should have an 'also' or 'too' in the second part

I will rest atstay home that day.

what you have is correct but 'stay home' is more idiomatic to say 'do nothing.' 'Resting' could make it sound like you're sick or injured or something.

I'm alsoBut now, I'm looking forward to thise holiday now.

unclear exactly what you mean. Nothing grammatically incorrect but this sentence's job is unclear. I reworded it to sound more natural

It has been a little busy this week, but I canould feel tha more relaxationing mood after today's lunchtime.

I changed can to could to maintain the past tense. You can't really "feel" relaxation so I changed the sentence a little.

I will rest at home that day.

This is not incorrect, but it would sound more natural to say "I will be resting at home that day."

It has been a little busy this week, but I canould feel the relaxationeveryone starting to relax after today's lunchtime.

You can essentially perform a direct translation from the native text.

It's lovely to hike in this season.

Alternatively, if you want to emphasise just how lovely hiking is, you can write "Hiking in this season is just the best." "lovely" does come across as milder, and loses some of the emotion.

It has been a little busy this week, but I can feel the relaxationed after today's lunchtime.

I'm also looking forward to this holiday now.