The synonyms of '雨后送伞' The phrase '雨后送伞' means unnecessary assistance.

[释义]    比喻事后献殷勤。也比喻帮助不及时。

Is there better phrases or idiom to express such a context?
How about

贼过兴兵

mobilize the troops after the bandits had gone

Meaning: fail to provide assistance timely; present unhelpful, useless, belated action