You can communicate like this and have it be effective if you have an established good relationship with the recipient. That’s why team cohesiveness is important.
Context of whom you are communicating with is also important. That’s the trade off of approaches like these rules. In some situations they are fine. In others not so much.
A rule that has suited me well is to take an estimate, double it, and increase by an order of magnitude for inexperienced developers.
So a task the say would take two weeks ends up being 4 months.
For experienced developers, halve the estimate and increase by an order of magnitude. So your 10 days estimate would be 5 weeks.
You have to be careful of the perceived politics around this. Tall poppies get cut down. I still don’t totally understand why but sometimes taking initiative doesn’t sit well with the folks who want their trains to run on time.