I'm going to haveon a one-day travelip to Suzhou City tomorrow.

Better to say trip instead of travel here. If you were to use travel as a noun, it would usually be "travels" (for example, "During my travels around the world, I have learnt many things.") But generally, "trip" would be the safer option.
"Going on" would also be a better way to phrase this (as in "going on holidays")

My train ticket is for around 9:30 and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out around 8:20.

The return ticket is at 19:50, but I need to spend 45 minutes to get to the train station, which means I need to finish everything before 18:30.

The "to spend" just sounded a little weird and unnecessary to me.

I'm going to havtake a one-day travelip to Suzhou (City) tomorrow.

“Travel” isn’t very often used as a countable noun, and “have a travel” sounds unnatural to my American ears.

“Day trip” is an excellent suggestion:
- I’m taking a day trip to Suzhou tomorrow.
- I’m going on a day trip to Suzhou tomorrow.

I don’t think it’s necessary to add “City” after Suzhou.

My train ticket is around {9:30 a.m. | 09:30} and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out around 8:20.

Your original is also OK, since the reader doesn’t have to think very hard to realize that, for a day trip, you’d be leaving at 9:30 in the morning, not at night.

A One-dDay Trip

NOTE: In some styles, you could also write "A one-day trip." [Different styles of capitalization exist in English.]

I'm going to have/take a one-day travel to Suzhou City tomorrow.

My train ticket iis/leaves around 9:30 and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out around 8:20.

One-dDay Trip

I'm going to havtake a one-day travelip to Suzhou City tomorrow.

If you say "day trip," it's clear that you will return home on the same day. "One-day trip" might mean you're spending the night there.

My train ticket isdeparts at around 9:30, and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out at roundghly 8:20.

Then I can have arboundt 40 minutes to check in at the station -- it', which is long enough even if the station is busyon busy days.

Sorry that I'm changing "around" so often xD
English avoids repeating words too often

The distance from Shanghai to Suzhou is aroundpprox. 85 km, so Iit will take 25 minutes to reach Suzhou Station in 25 minutes.

TheMy return ticket is atset for 19:50, but I need to spenwould probably need 45 minutes to get to the train station, which means I need to finish everything before 18:30.

I'm going to haveon a one-day travel to Suzhou City tomorrow.

My train ticket is for around 9:30 and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out at around 8:20.

Then I canwill have around 40 minutes to check in at the station -- it's longThat will be enough time even if the station is busy.

The distance from Shanghai to Suzhou is around 85 km, so I willand it takes 25 minutes to reach Suzhou Station in 25 minutes.

The return ticket is atfor 19:50, but I need to spendit will take me 45 minutes to get to the train station, which means I'll need to finish everything before 18:30.

I'm going to haveon a one-day travelip to Suzhou City tomorrow.

My train ticket is aroundis at 9:30 and the train station is not far from my apartment, so I'll sleep in tomorrow morning and head out around 8:20.

Then I canwill have around 40 minutes to check in at the station -- it's long enough time even if the station is busy.

The return ticketrip is at 19:50, but I need to spendit will take me 45 minutes to get to the train station, which means I need to finish everything before 18:30.