The answer is very little to NONE on a daily basis excluding self inflicted delays.
There are two reasons to have to work under undo external pressure.
Both can be mitigated.
1) Incompetent Management promising unrealistic goals.
2) Incompetent Developers unable to meet realistic goals.
Both can exist at the same time. Neither should have to.
Agile Methodologies, SCRUM in particular can help mitigate these issues to a great extent. The management lets the development team decided what they can reasonably commit to in a single Sprint ( 1 or 2 weeks at most ). Even a very junior development team can learn to estimate what they can accomplish as a team in 1 or 2 weeks.
Agile Methodolgoies also focus heavily on what is of business value to the customer. Clean code, maintainability, best practices, etc. isn't of high value to some customers or some projects.
It depends on the product and the customers desires, if the product owner explains to the customer you can hack something together in 2 weeks that has limitations, but have to go and redo it later to remove those limitations, there is nothing wrong with that. It is technical debt, and it is documented and managed.
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
That is, while there is value in the
items on the right, we value the items
on the left more.