That site seems to be more oriented towards tourist interests than to Weather (which is the aim of Windy.com).
On a Weather site, these cams would rather make big noise instead providing pertinent Weather info...
I checked a couple of dozens of cams in Ireland and England, and all images have a timestamp.
Would you have some case study where they don't?
If some 3rd party webcams don't send timestamps, I would not blame Windy programmers: they could not help here.