Delete_many on nested documents with pymongo

Hello guys.I want to delete some of my documents.My collections look like this:

{
	"_id" : ObjectId("608d84777791538ce2a09f2f"),
	"nsamples" : 288,
	"samples" : [
		{
			"20" : ISODate("1980-01-01T00:00:00Z"),
			"1" : 3758,
			"2" : 2,
			"3" : -79.09,
			"4" : 35.97,
			"5" : 5.5,
			"6" : 0,
			"7" : -99999,
			"8" : 0,
			"9" : -9999,
			"10" : "U",
			"11" : 0,
			"12" : 99,
			"13" : 0,
			"14" : -99,
			"15" : -9999,
			"16" : 33,
			"17" : 0,
			"18" : -99,
			"19" : 0,
			"21" : "2009-12-31 19:05:00"
		},
		{
			"20" : ISODate("1980-01-01T00:05:00Z"),
			"1" : 3758,
			"2" : 2,
			"3" : -79.09,
			"4" : 35.97,
			"5" : 5.5,
			"6" : 0,
			"7" : -99999,
			"8" : 0,
			"9" : -9999,
			"10" : "U",
			"11" : 0,
			"12" : 99,
			"13" : 0,
			"14" : -99,
			"15" : -9999,
			"16" : 33,
			"17" : 0,
			"18" : -99,
			"19" : 0,
			"21" : "2009-12-31 19:05:00"
		},
               .
               .
               .               
               .

The query i am trying to execute is this:

    mydb1.insertion_testbucket.delete_many({"samples.20": {"$lt": datetime.strptime("1980-01-01 02:00:00", "%Y-%m-%d %H:%M:%S")}})

I only want to delete some of the nested subdocuments in the first document,and not the whole first document.Is this the right way?

I want your advice before i execute it.Thanks in advance guys!