If it doubles the amount of water in the tank every minute that must mean there was some water in the tank to begin with or it will never fill. :3
But ignoring this flaw, since it's obvious you're intended on working backwards - since it doubles every minute then after 28 minutes it will only need to double twice more to fill (thus making it 1/4 full). So the answer is 28 minutes...
Good idea for a thread by the way - if you can manage to commit the time and thought to it. :/

28 minutes elapsed.
But I woke up too late to get it first, ._.
And for me this is early. -.-

Looks like there's a new sheriff in town...or y'know...puzzle solving guy >:3
EDIT: Warning! Video might scare people.

Whatever, it's no big deal. And I did say this would happen.
Also that video kinda scares me. O_O

That's ok bro - I got you covered.
Made a warning edit on the original post. >:3

._." Uh... Ok.

@Geonjaha That was pretty funny! . Reminds me a lot of the awesome series. :3

dang i was way to late i forgot to get on this morning!

@Geonjaha Yup, that's right! :3 Also, sorry for the flaw, it was 6:30 in the morning here .
And I have the commitment to this, and usually the time. Although due to traveling / vacations I may miss about 30 days a year, but I'll set someone up to post the puzzles.
You're officially on the scoreboard now~
@Tri @Skit You'll get more points. Just have patience.

Puzzle #7

One morning you are working at a fancy pancake restaurant. Your job is to store all of the boxes of batter for the pancakes. This requires moving them all from a seperate garage, over to the restaurant.

It takes:
1 minute to carry a small box.
2 minutes to carry a medium box.
4 minutes to carry a large box.
The time it takes to walk back is 1 minute.
(Note: If you are carrying 1 small box and a large box together, it will take the time of the larger box to carry both.)

Today you need to transport 5 large boxes, 7 medium boxes, and 12 small boxes. You can carry 2 boxes at a time, but never 2 large boxes. What is the fastest time you can accomplish this in?
(Please explain your answer. The person with the lowest time before the next puzzle is uploaded will win.)

How long does it take to carry 2 medium-sized boxes?

There are 24 total boxes and if I can carry two at a time then that means I'll do 12 trips back if I'm carrying 2 at a time. (12)
Then I carry a big and a medium so then it'll take 20 minutes to get rid of all the big boxes, and I'll get rid of 5 of the medium boxes, so then I'll have 2 mediums remaining, so I'll take the mediums with each other,, so12 small boxes two at a time so then 6 minutes.
12+20+2+6=40 minutes, I think. ._.

_{knowing myself I'm definitely wrong on this, and I didn't do a good job at explaining either.}

Get rid of the large boxes first along with as many medium boxes as possible because they don't affect the time.
5*4 (+5 for returning) = 25 mins
Next carry the 2 leftover medium boxes along with each other.
2 (+1 for returning) = 3 mins
Then carry the remaining 12 small boxes, 2 at a time.
6*1 (+5 for returning [YOU FINISH BEFORE YOU RETURN FOR MORE BOXES]) = 11 mins

25+3+11 = 39 mins.

Just in case people cant get in the mood. :3

A fairy an elf and a tingle are on trial, all accused of stealing 1,000 en from the bank. The fairy is wearing a flowing white dress that comes down to her ankles with a soft pink bow at her chest and a sunhat. The elf has on a vest woven from large leaves from the forest with breeches and tree bark boots. The tingle has on a skin tight green jumpsuit. Who stole the money?

Oh yeah, I didn't think about that @geonjaha, nice job, though I did see all the fail math earlier, I was wondering how you got 30 minutes.
I was going to change my answer because you pointed it out but still thought it was 29 but decided not to because I'd feel cheaty, but then you changed it to what I would've done. :/
_{im sad on the inside}

Smexi, what are you talking about!?

I rushed and failed because I misread my own post. X3 (25 as 15)
You have too little faith in yourself.

faith in myself isn't something I do well.

Your'e all wrong it's 34... 20+4+10=34
Exclusive the coffee break
EDIT: oh wait miss calculation ._."

And walking back. :/ +5 minutes because you're walking back, and finishing at the end and not requiring walking back.