In personal finance, a time horizon is how long you expect to stay invested before you need the money. The SEC's investor site puts it simply: the number of months, years or decades you need to invest to reach a goal. The longer the horizon, the more volatility you can sit through on the way.
On Javlot the word is used for the strategy rather than for you. Every strategy carries a horizon tag, short, mid or long, and it answers one question: over what stretch of time do its results mean something? A short-horizon strategy turns its capital over quickly, so a few weeks of history already say a lot. A mid-horizon strategy needs months, because its positions and its cycles take that long to play out. A long-horizon strategy asks for a year or more, and judging it on a bad quarter is judging it on noise.
The tag is set by the editorial team from the strategy's style and its track record, and it is meant to be read together with the drawdown. A long horizon and a deep drawdown tell you what the wait can feel like before it pays.
Nothing about the horizon changes how the strategy is copied. It changes how patient a subscriber should plan to be, and how much of the equity curve is worth looking at before deciding whether it works.