I think the distance is easier to measure than the time, but they’re both correlated. It takes light a year to travel one lightyear, so a galaxy that’s 40B lightyears away should require 40B years for that light to reach us, while we operate within a model that says the universe began only 14B years ago (not possible for light to travel 40B light years in 14B years). I guess I still don’t have an immediate answer to your question, I know that red- and blue-shifting of light helps us tell how fast a galaxy is moving away from or toward us, respectively, but I assume they’re able to compare one galaxy to another and gauge the distance away that one must be versus the other, allowing us to “ladder” the distances from one galaxy to the next. At a minimum, anyway. Regardless, they confidently tell us that they imaged a galaxy 100 billion light years away, and that that can only happen within a 14 billion year timespan because space has expanded and moved that galaxy away from us faster than the speed of light, though that isn’t directly accounted for in Einstein’s theory of general relativity. It’s just an adjustment we’ve made because without the adjustment, the theory would have to be wrong