The increase in distance would be approx. 6,000Nm (assuming they arrived at the entrance to the Red Sea before having to change course).
6000Nm and, say, 25 knots (probably a bit on the high side, but not by much) should add 240 hours of steaming or 10 days to the voyage.
(This will be somewhat offset by the lower speed through the channel, waiting times &c - I've no idea how long a typical Suez transit is.)
