Have you ever held something in for weeks or months before you finally let someone know what was on your mind? You wouldn’t be the first person to do that, but it’s never the best way to go (trust me, I speak from experience).
When you hold off, minor issues can grow into major ones, and the person receiving the critique is more likely to become defensive if you start pointing out problems that stretch back weeks, months, or years. You’ve also robbed them of the opportunity to make an improvement the entire time you’ve held back your feedback.
Plus, it’s just easier to solve problems when you address them quickly. In the U.S., we call it ‘ripping off the BAND-AID’. The idea is that peeling a BAND-AID off slowly is far more painful (physically and emotionally) than giving it one firm yank.
Of course, don’t be in such a hurry that you send the message via email or text. Written communication carries far less nuance than spoken communication, and in my experience, you can convey more context verbally. That way, they won’t take your words in ways you never intended. Instead, have a live conversation if at all possible (in person, over video chat, or on the phone).