A phrase used to express when you'd like for someone to do something, but you don't want them to feel pressure to do it immediately or to feel burdened by it; rather, whenever they have the chance or if they can.
It is also used to express when you're not intending to pressure someone or to soften a request you have for someone so that it doesn't feel hard, harsh, or demanding.
It can also be used sarcastically, in an event when there really IS pressure to so something.
Hey, call me whenever you decide. No pressure.
Said sarcastically to an instruction to carry out something with great significance. The full meaning being "so I'm under no pressure then", when clearly you are.
"If you don't defuse the bomb millions of people will die"
There is no problem between you and someone else. You're not holding anything against them and there's no need for drama.
Wathson:So you got a problem with me?
Sandra: No there ain't no pressure. You good.