You are correct - the only way to gain rep with a crafting guild is through the turn-ins
If you have all the tiers open and are diligent about making them when they come off cooldown the earliest you can make kindred is 15 days, however if you save up the large symbols (the ones with 1 week cooldown) so you can make the jewellery as soon as you have enough rep then it will take 19 days.
By waiting the extra 4 days you save up 2 each of the large master and large supreme tokens to give you a nice headstart on the the jewellery.
Don't forget that once you make kindred, you may still want to make the Small/Medium symbols for T5 and T6 because although they have limited/no use in recipes they can be traded up for Med/Large symbols.
Here's a chart I made a while ago to help illustrate the timeline.