Reasonable response time to a complaint email?

[321gogogo]

Emailed a teacher with a complaint about another teacher on Friday.
This morning I emailed the executive head of KS 3...
No reply to either
How long do you reasonably think I should give them before I go up the chain?

Do you know whether the person you emailed was in on Friday? Or today? They might be unwell, on a course, run ragged with other matters.
If it needs to be answered before tomorrow, forward it to whoever is the immediate senior to the person you contacted and ask them to pick it up.