Change Genbank entry date with Biopython
So, the problem is that you are probably using wrong class for your record. Compare Bio.SeqRecord class with Bio.GenBank.Record class. Reason why in your GenBank format you have this reference date (01-JAN-1980) is because your record has intrinsically no date attribute, so SeqRecord.format set undefined fields to default (look through the source code to see where this happens).

What you want to do for creating GenBank record is following:

$ python
Python 2.7.10 |Anaconda 2.3.0 (x86_64)| (default, May 28 2015, 17:04:42) 
[GCC 4.2.1 (Apple Inc. build 5577)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
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&gt;&gt;&gt; from Bio import GenBank
&gt;&gt;&gt; from Bio.GenBank import Record
&gt;&gt;&gt; my_rec = Record.Record()
&gt;&gt;&gt; my_rec
&lt;Bio.GenBank.Record.Record object at 0x1030b1890&gt;
&gt;&gt;&gt; my_rec.sequence = Seq(my_sequence)
&gt;&gt;&gt; my_rec.sequence
Seq('ATAGGGACUCATAGATA', Alphabet())
&gt;&gt;&gt; print(my_rec)
LOCUS                         bp                                         
DEFINITION  .
KEYWORDS    .
SOURCE      .
  ORGANISM  .
            .
ORIGIN      
        1 atagggacuc atagata
//
&gt;&gt;&gt; my_rec.date = '13-JUL-2015'
&gt;&gt;&gt; my_rec.features.append(my_feature)
&gt;&gt;&gt; my_rec.data_file_division = "ROD"
&gt;&gt;&gt; print(my_rec)
LOCUS                         bp                    ROD       13-JUL-2015
DEFINITION  .
KEYWORDS    .
SOURCE      .
  ORGANISM  .
            .
FEATURES             Location/Qualifiers
type: CDS
location: [2:5](+)
id: Cre
qualifiers:
    Key: foo, Value: bar
ORIGIN      
        1 atagggacuc atagata
//


Notice, how print(my_seq) outputs data in GenBank format by default (since that is a GenBank record after all). I am sorry I cannot really talk on differences between GenBank.Record and Bio.SeqRecord and why/when use one object or another.

Anyways, looking up reference documentation is always a good habit: http://biopython.org/DIST/docs/api/Bio.GenBank.Record.Record-class.html