Advice please, 1 unhatched egg.

[ChickNZ18]

In New Zealand just entered spring.
I had 4 of 5 fertile eggs hatch
First hatched a good 72hours ago last one hatch 24hours ago.
How much longer should I leave with her or is time to attempt help (It's possible a silkie cross)

 

[ChickNZ18]

 

[ChickNZ18]

I candled egg, was all slushy with no specific air sack just a moving bubble
So opened it, its only a tiny embryo about 1/2tsp size so I'm glad I checked and didn't leave poor mumma sitting on it.