Let's look at the first set and the first value.
First[Normal[TimeSeries[Databin["7j5P9Pz2"]]["temp1"]]]
To see what the actual value is, use InputForm. This will show you exactly what the first element is.
{{2015, 10, 3, 21, 29, 30.087313175201416}, "74.20"}
When you make a Databin, it will assume everything is a string unless you specify some kind of type, like "Number". Here is how work aroudn the current problem:
(* get the data as a simple list of values *)
data = Normal[TimeSeries[Databin["7j5P9Pz2"]]["temp1"]]
(* turn the temps from strings into numbers *)
data = data /. {date_, temp_} :> {date, ToExpression@temp}
(* alternatively you could turn the temps from strings into numbers this way *)
data = MapAt[ToExpression, data, {All, 2}]
DateListPlot will now work with the variable "data".
