I might give it an extra 20% or so. For instance, Ilford recommends 4-5 minutes in HC at 1+15, depending on your intended contrast. So I'd go for 6 minutes at that dilution. I'd do the same math at higher dilutions, or for any other developer for that matter. Alternatively, you really can develop this film under a dim red safe light. I have done so. It works fine and is fun as well.
I have only experimented with Ortho 80 a little, but from what I have seen so far I rather like it. Contrast is not crazy at all, and is controllable through development as with any other film. It reminds me of FP4 without red sensitivity. I like how bold clouds look with a deep yellow filter (and yes, filter factors are different due to the ortho sensitivity, as mentioned on the data sheet).
There is another odd remark on the data sheet recommending processing within 1 month - three times worse than with PanF 50, which is known to have latent image retention problems. I had an exposed 120 roll I'd forgotten about, and by the time I found it and read the data sheet 8 months later I was worried it would be a total loss. Not so - not even close it turns out. That roll was developed under a red light in Rodinal 1+50. Really nice negatives - crisp and clean looking with excellent shadows and highlights. They remind me a lot of the 70+ year old Verichrome negatives my grandfather gave me. The 1-month warning is no longer a concern.
Anyhow, don't sweat it too much. I believe Ortho 80 is a flexible film with very good latitude. That extra 20% will keep your shadows up, and I doubt do much damage to the highlights. Everyone has their own preferences, but I'd much rather err on the side of more development than not enough.