Accepted answer

Sounds like you want to group by ID and then convert to a dictionary, so that you end up with one dictionary entry per ID:

var dictionary = entries.GroupBy(x => x.ID)
                        .ToDictionary(g => g.Key,
                                      // Find the earliest time for each group
                                      g => g.Min(x => x.Time));


                         // Group by ID, with each value being the time
var dictionary = entries.GroupBy(x => x.ID, x => x.Time)
                         // Find the earliest value in each group
                        .ToDictionary(g => g.Key, g => g.Min())

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