The park is closed at night - see the Lee Valley Regional Park website for opening times and also details of wildlife you might see.
There is CCTV in the park due to the DLR but I can't see any covering this spot - you don't need to do anything that should cause alarm - the cache is not attached to the DLR side.
Like Lyle Park, this is one of those spaces that seems to be used less than it might deserve - though many will have passed through it on the DLR and some may have been here before caching: GC1GDN7. I hope you enjoy it.