The date pattern "dd MMM yyyy;HH:mm:ss.SSS" obviously doesn't match the actual time format "2017-08-10_18:11:40.461". You'll have to rearrange things a little bit. See the date filter documentation for details on what the various pieces of the date pattern mean.
Also, you are using a json codec or filter to process the input, right, so that there actually is a Time field to parse?