Well...what was your recipe? What yeast did you use? Any additional sugars? Do you have a hydrometer? What EXACTLY did you do and how long has it been on?
A hydrometer reading will help most of anything, because then the answer is-the primary fermentation is down when the specific gravity stays static for a prolonged period. (I use at least a week of no change, sometimes two if it's been a problem ferment)
Or you can use the mead calculator, a handy dandy link on the left hand side of the page, to figure out an approximate original gravity, ABV, so on and so forth. You can use the yeast tolerance and the OG to figure out where your yeasties SHOULD poop out according to the SG, but don't trust that till you have no static change for a while.
If you have no hydrometer and are completely guessing with no airlock...um, much harder. Some ferments are over in under 5 days, some, really sucky ferments, can take almost 2 weeks. And I've got one or two that have a completely static SG with no change whatsoever for two months, and it still has visible signs of fermentation. (My lemonade and 5 gal coffee come to mind, both are still bubbling)
If you really have no other way to check, wait two weeks, and then move it to secondary...but I'd get an airlock and seal on that as soon as possible. Without the blanket of CO2 being produced by an active ferment, you're opening up the mead to oxidation and spoilage organisms with the towel. People who do the open ferment like this use the hydrometer daily to keep track of the process.
Btw, welcome to the addic...er, HOBBY!