How to search list elements in a data frame?

I have a list dates with dates as string objects with all dates from 2003-01-01 to 2017-06-30:

['2003-01-01', '2003-01-02', '2003-01-03', '2003-01-04', '2003-01-05', '2003-01-06', '2003-01-07', '2003-01-08', '2003-01-09', '2003-01-10', '2003-01-11', '2003-01-12', '2003-01-13', '2003-01-14', '2003-01-15', '2003-01-16', '2003-01-17', '2003-01-18', '2003-01-19', '2003-01-20', '2003-01-21',...]

And I have a dataframe with date time objects:

0       2013-01-09 09:07:49
1       2013-01-09 09:16:25
2       2013-01-09 11:14:28
3       2013-01-09 11:25:51
4       2013-01-09 11:25:51
5       2013-01-09 11:33:35
6       2013-01-09 11:35:31
7       2013-01-09 18:11:03
8       2013-03-13 21:04:58
9       2013-03-13 21:05:57
10      2013-03-15 14:07:27
11      2013-03-26 21:53:35
12      2013-03-26 22:19:20
13      2013-04-09 14:21:48
14      2013-04-09 14:22:29
15      2013-04-09 14:22:45
16      2013-04-22 12:10:47
...

Then I want to check if the dates in the list dates exist in the dataframe. So I want to do something like this:

df = pd.read_csv("blabla.csv")
df['time'] = pd.to_datetime(df['time'])
for j in dates:
  if j in df['time']:
       return(yes)

How can I compare a string object with a datetime object in a dataframe?