[brokensegue]

investing implies a long term horizon. if you are just taking advantage of an arbitrage opportunity then you are a commodity distributor/shipper or commodity trader. you aren't investing in the underlying asset you want to hold the asset for as short a period as possible to avoid the arbitrage disappearing beneath you.

[MR4D]

Investing implies no such time horizon.

Investing is spending money with an expectation of a return.

For contrast, expenses have no expected return.

Neither have a time horizon. And further, what would “long term” be anyway? Not sure how you could ever define it.