Inertial vs Transport Delays

Inertial Timing 
ENTITY nand2 IS
    PORT(A, B:IN bit; C:OUT bit);
END nand2;

ARCHITECTURE behaviour OF nand2 IS
BEGIN
    C <= not(A and B) AFTER 25ns;
END behaviour;
Transport Timing

ENTITY nand2 IS
    PORT(A, B:IN bit; C:OUT bit);
END nand2;

ARCHITECTURE behaviour OF nand2 IS
BEGIN
    C <= TRANSPORT not(A and B) AFTER 25 ns;
END behaviour;