Sit tight
Definition 1 of 2
Pro Tip 1/3Expect Delays
Use 'sit tight' when you need to wait, especially if there's a delay or nothing else can be done. 
The flight is delayed due to the storm, so we'll just have to sit tight.
Pro Tip 2/3No Immediate Action
'Sit tight' suggests remaining calm and patient, without taking immediate action. 
There's a power outage; just sit tight until the lights come back on.
Pro Tip 3/3Temporarily Static
It often points to a temporary state where one stays put or inactive for a while. 
Sit tight until I return with more instructions.