We would like information about the limit of The Things Stack Sandbox free plan. We are wondering if the limit of 10 devices and 10 gateways refers to those that are online at a given time, those that connected in the last hour, or if it also includes those that have performed a join within the 10 teams allowed.
Forum volunteers do not have a definitive answer and views vary! - in part to stop people gaming the system. Your best option is raise the question on the #support channel of the TTN Slack where it is more likely to be picked up by TTI staffers. Of course you could alsways contact TTI sales and ask directly - it seems you have an underlying reason for asking the question and may also have a commercial imperative? (Community limits are looser for genuine projects 
)
Without you explaining your intent there is no context to be able to provide guidance.
If you are trialing a system to keep kittens safe there’s one answer, if you are using it to track the personal biro’s of billionaires, there’s another.