1. What does it mean?
짐 can shorten 지금 in casual messages, particularly when arranging where to meet or saying what you are doing at the moment.
Also written or said as jim
2. The nuance
Outside that texting use, 짐 ordinarily means baggage or a burden. In 짐 챙겨, it is probably luggage; in 짐 도착, it is likely 'arriving now.'
3. Examples
“나 짐 역에 도착했어. 천천히 와.”
I've just arrived at the station. Take your time.
“짐 통화는 어렵고 한 시간 뒤에는 괜찮아.”
I can't talk right now, but an hour from now is fine.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.