“改天请你吃饭！”——这个“改天”，通常是哪天？
“I'll treat you to dinner 改天 (another day)!” When is 改天, usually?
全球翻车率（内测预估）
A农历的改天节
nóng lì de gǎi tiān jié · "Another Day", a lunar-calendar festival
✓不会到来的那天
bú huì dào lái de nà tiān · a vague day that will probably never come
C就在这个周末前后
jiù zài zhè ge zhōu mò qián hòu · this weekend
D明后天之内
míng hòu tiān zhī nèi · tomorrow
“改天”和“下次一定”，中文世界最大的两张空头支票，且永不兑付。
改天 (“another day”) is a warm way to close a conversation, not an actual plan. If they mean it, a date follows immediately.