Should I meditate during a stressful moment or wait until I've calmed down?

During, if you can. A 2-minute breathing reset between meetings or before a difficult conversation is more effective than a 20-minute session at the end of the day. In-the-moment meditation catches stress before it compounds. That said, some stressful situations don’t allow for meditation (you can’t close your eyes in a tense meeting). In those cases, even awareness of your breathing — without formally meditating — helps. And yes, end-of-day decompression meditation still has value. The best approach is both: micro-practices during stress, longer sessions to process it afterward.