You need to be planning for a maximum packet rate of around 120 secs for fair access limits.
Your application does not seem possible under TTN, although you could ask TTI and see how much it would cost to use that amount of backend resource.
how long could be the minimum time between sending one packet and the next, without losing data between packets with my MKRWAN 1300 sensor (Arduino).
Not sure how anyone can reply to that, without knowing what ‘square wave’ you are monitoring, what data you are collecting, and why you are collecting the data.
Note the MKRWAN 1300 and indeed the Murata CMWX1ZZABZ it uses is Sub-GHz operation only - it does not support 2.4Ghz LoRa/LoRaWAN operation so you would need other hardware. Good luck with that as 2.4Ghz LoRaWAN ecosystem is still very small and limited at the moment…
Not really the wording we use - uplink frequency (which is confusing with the radio bit) or period or how often, or delay. And not package - payload is the data, uplink is the whole thing.
But it doesn’t really matter how far apart they are, the point is, as explained more than a few times plus the link to the airtime calculator which spells out what you can do, or not, it’s the total air time you consume, not how often.
We are still non the wiser as to what the data is, how big it is, how often you actually need it to be, but I suspect by the time you give us a clue, the volunteers (that’s everyone on here) will have lost the will to respond. So I’d strongly recommend that you make your next post on point - answer the questions, use the calculator and take the hint from me & Jeff about the 2.4GHz radios etc etc