According to SaaStr, the timeframe to assess a new sales rep is 1.0 to 1.5 sales cycles. The publication states that leaders will often know the outcome sooner.
SaaStr reports that the best reps get on the board by closing 1 or 2 deals early, even if they do not hit quota immediately. If no progress appears in 0.5 to 1 sales cycles, the outcome rarely improves. The source notes that sales reps begin to lose confidence when early wins do not materialize.