No doubt 2 Donkeys will be along shortly to remind you that there is no "Day" restriction. It's simply restricted to VFR.
You're doing my job for me!
There is actually no VFR-only restriction either. The holder of an ICAO IR (of which the FAA's IR is an example) is entitled to fly under IFR outside controlled airspace in the UK in a G-reg (regardless of weather conditions), without further ado.
This is quite separate from being able to apply for an IMC rating.
2D