c-objc-method-arg-min-delta-to-bracket is a variable defined in `cc-vars.el'.
Its value is

*Minimum number of chars to the opening bracket.

Consider this ObjC snippet:

[foo blahBlah: fred
|<-x->|barBaz: barney

If `x' is less than this number then `c-lineup-ObjC-method-call-colons'
will defer the indentation decision to the next function. By default
this is `c-lineup-ObjC-method-call', which would align it like:

[foo blahBlahBlah: fred
thisIsTooDamnLong: barney

This behavior can be overridden by customizing the indentation of
`objc-method-call-cont' in the "objc" style.

You can customize this variable.