Unistrut Spacing - Electrical Conduit
Support is required as specified for the conduit - unistrut does not make any difference in the required support spacing.

For EMT, the required support is within 3 feet of each termination, and a minimum of every 10 feet.

I'm not as familiar with the support requirements for rigid, it's too rich for my blood. Whatever they are, they are not influenced by the support being unistrut.