It's not so much the time but the conditions that make for needing to replace the bolts. If your bilge
has historically cycled from wet to dry, that can be a bad sign as is just remaining wet.
There are a couple of things that concern me in photo
. I don't see any sort of corrosion
inhibitor and the bolts seems rusty. Neither are absolute indicators but they do concern me.
I'd start by looking on the outside of your boat, if possible. If you see rust weeping, that's a bad sign as you have a compromised seal and might can have crevice corrosion
of the bolts making the appearance issue a moot point. If that's not a problem, try loosening one bolt and then tightening it. If it moves fairly easily, it's more likely the rust minor and or recent. Coat with an anti-corrosive coating, keep the bilge
dry and sail on.
If not, you need to figure out where on the risk spectrum you are. You don't have to replace it and in fact it probably does not make sense if you do mostly day sails
in goodish weather
Hope that helps,