You will not get the same daily each day. If you manage to do that more than 2 days in a row then it is RNG favoring you.
This is the same exploit people used (and still use) to get double weapon dailies at Argent Tournament. In fact, your effort is better spent there for the extra weapon daily (works 66% of the time) unless you really want Jewel of the Sewer again or something.
How it works is the time when the server resets your daily quests is slightly different than the time when the dailies actually change on the NPCs. So, there is about a 10 second window where you can pick up the previous day's daily before the RNG picks a new daily for that day. Sadly you can't do 2 fishing dailies or 2 cooking dailies because they are all lumped into the same category. However, the weapons dailies are not (and I heard that the polar bear mount dailies aren't, either). So, if the next day's daily is different from the previous, you could get 2 dailies instead of 1.
Hope that clarifies things for you! I know I used it to get to Champion several days every everybody else!
Looks like, that it's working.
Was just curious bout this, so I checked the cooking and fishing daily after the reset (announce in chat) and had the same quests than yesterday.
I only accepted the cooking one, run around Dalaran, collecting the wild mustard and went again to the fishing daily NPC.
She gave me "Blood is Thicker" on 03:01 am, had "Dangerously Delicious" the last day..
Tested it today... so far so good. I'll try again tomorrow and see if I still can get back the same cooking and fishing quest.
Ahh this happened to me on the giant women dailys ALTHOUGH when I tried to accept the quest it said I wasn't eligible and i tried again gave me a different daily and I went and did that. I was camping the daily spot waiting for them to reset so i was near next to immediate.