Just use the second item of the tuple as a secondary priority if a alphanumeric sort on your string data isn't appropriate. A date/time priority would give you a priority queue that falls back to a FIFIO queue when you have multiple items with the same priority. Here's some example code with just a secondary numeric priority. Using a datetime value in the second position is a pretty trivial change, but feel free to poke me in comments if you're not able to get it working.

Code

import Queue as queue

prio_queue = queue.PriorityQueue()
prio_queue.put((2, 8, 'super blah'))
prio_queue.put((1, 4, 'Some thing'))
prio_queue.put((1, 3, 'This thing would come after Some Thing if we sorted by this text entry'))
prio_queue.put((5, 1, 'blah'))

while not prio_queue.empty():
    item = prio_queue.get()
    print('%s.%s - %s' % item)

Output

1.3 - This thing would come after Some Thing if we didn't add a secondary priority
1.4 - Some thing
2.8 - super blah
5.1 - blah

Edit

Here's what it looks like if you use a timestamp to fake FIFO as a secondary priority using a date. I say fake because it's only approximately FIFO as entries that are added very close in time to one another may not come out exactly FIFO. I added a short sleep so this simple example works out in a reasonable way. Hopefully this helps as another example of how you might get the ordering you're after.

import Queue as queue
import time

prio_queue = queue.PriorityQueue()
prio_queue.put((2, time.time(), 'super blah'))
time.sleep(0.1)
prio_queue.put((1, time.time(), 'This thing would come after Some Thing if we sorted by this text entry'))
time.sleep(0.1)
prio_queue.put((1, time.time(), 'Some thing'))
time.sleep(0.1)
prio_queue.put((5, time.time(), 'blah'))

while not prio_queue.empty():
    item = prio_queue.get()
    print('%s.%s - %s' % item)