Logistical orders in Aurora are a WIP. Frankly it is a complicated topic since there are a lot of situational details that need to be accommodated to make it work well. For gas miners the workaround I've been using is to give the miner 15-20% more fuel capacity than the tanker, set up an order template, and then fire it off manually every time the miner reports that it is over 90% full. Not ideal but it works.
My harvesters are kinda "tiny" but many. They fit in my standard civilian ship size of ~35k so that my tugs can move them with their jump drives. I guess later on I will increase my standard size to build larger ships to fit massive sized engines, but for now I would need a gazilion tankers to get it done this way. But the tankers are designed with much larger fuel reserves as the military drives are the thirsty kind 
Thanks guys. I had thought about some time delay, but it seemed like a hassle since I'm regularly shipping more harvesters. It looks like that the most convenient way to handle this then would be to design mobile harvesters when harvesting in a system with a colony. It's less efficient but a handful days not harvesting every now and then wouldn't be that bad.
Oh well. The calculation shouldn't be that hard. 15 million litres for the tanker, 576k litres per annum from the stations, so with one trip a year, the tanker can handle more than 26 stations. I have 16 harvesters, so that's 1.6 times 26, so a back and forth trip every 1.6 year should do. I want it to be done with 75% full tanks for conveniency sake, so a trip every 1.2 years, that will be a 38 434 500 delay. I'm not even losing that much fuel, a back and forth trip only requires 0.05% of the tanker capacity so I'm not wasting a significant portion of my fuel output.
Yes, that wasn't that bad. The real trick for "manual" automation though would be to come up with a formula to calculate how much to shorten the delay every time I add an harvester... looks a bit more complicated, that's too much maths for now
To preserve sanity, don't try for perfectly efficient operations.
Here's how I manage:
I have a class design I call Timer. It is just an empty, unarmored hull. Costs 0.4BP.
I SM-add one of these to a fleet around an unused planet (I don't want to it to cause visual clutter around worlds I am actively managing.)
On Jan-1, I give the fleet cycling orders to
1) Move to the planet it already orbits, with a 1-year delay (31536000 seconds)
2) Send a message: "Happy New Year!"
This gives me an event interrupt every Jan-1.
I have a checklist of things I look into on this interrupt. The rest of the year, I spend no time managing these things.
For example, fuel hauling tasks.
I append the annual harvesting rate (base, not including bonuses) to the name of each harvesting fleet. (E.g. "Harvesters - ADE-10 - 5.76ML")
I have cycling orders for tankers to retrieve fuel from the harvesting fleets. In the name of each hauling fleet, I include the annual hauling rate of the fleet. (E.g. "TK ADE-10 2.4ML/yr Tanky 007")
I set these up so that I'm hauling away most of the harvested fuel on a continual basis, but I try not to over commit tankers.
On Jan-1, I examine each fuel harvesting fleet.
If a fleet is currently holding a lot of fuel, I task a tanker to retrieve it. (This might be immediately (if I have an idle tanker), or it might go on my to-do list for the year.)
That's it for managing fuel harvesting.
