Partitioning key must be a column of the table being partitioned. If you have a correlation between id and datetime in timetable then you can partition by that id:
id datetime
1 20091001
2 20091002
3 20091003
...
32 20091101
33 20091102
...
62 20091201
...
then the partitioning ranges (2009-10-01, 2009-10-31), (2009-11-01, 2009-11-30) etc can be expressed in terms of id values: (1,31), (32,62), ... However, this requires that the rank of the id values matches exactly the rank of the datetime values. If you don't have this correlation, then you must either move the datetime column in the bigtable, or rearrange your id so that they correlate wqitht he datetime.