There is something a little "flaky" with it ..
In general I see about 75% of the beacons that I send out that I CAN see on aprs.fi get to outernet .
To answer your question, IF it picks it up, it usually broadcasts it as soon as it has finished the document it is sending .. so if it is 99% through a document when it "sees" your message it can be broadcast within a couple of minutes... if it has just started a big document, it can be quite a while (30 mins maybe).
As I said not all of them get there, despite being OK on APRS.fi and I have a theory about that which @syed may like to think about..
When a "one off" APRS message is seen by outernet, it creates a "messages" file to be transmitted , but it needs to wait as there is a file already being transmitted..
Then BEFORE the current file on the carousel is completed, a whole barrage of ISS APRS messages come in (as they do) and the outernet system either:
a) tries to append the new mass of messages to the existing "waiting" message file and it loses the original content, or
b) can't handle more than one waiting message file so overwrites or othewise loses the original one that had my message in it.
As a side note, it seems that the "message" file that only has one or two OUTNET messages in it is very,very small in size, so it IS possible to miss receiving it even if it was transmitted from the Sat if you have more than ZERO packet loss
I hope that helps
Just for the record I transmit hourly and/or random beacons from HF to OUTNET (usually 10.147Mhz) using either PSKMail (M0KNC-4) or good old fashioned AX25 at 300 baud (M0KNC-10) when I am not using my HF transceiver for something else. I believe it is interesting to have an HF "back channel"