From supermemo.guru

Cloze interval in SuperMemo is the first interval used by cloze deletions. Due to the fact that cloze deletions are often generated in larger numbers from a single sentence, paragraph or a longer topic, they cannot use the optimum first interval as it would cause inter-item interference. Several similar items scheduled on the same day will affect each other's performance with detriment to memory and to the performance of SuperMemo Algorithm.

This is why the first interval in cloze deletions is determined by choosing a random value from the first interval span that is determined by item's priority. High priority items will use short intervals (even 1 day). Low priority items may use intervals as long as 40 days. This often causes confusion as users of SuperMemo believe that the algorithm must be flawed for providing intervals that may yield very low retrievability.

The formulas used in determining the cloze interval have been derived empirically by years of testing of various solutions. They may feel unsatisfactory for new users. For this reasons, the user always has an option to choose the first interval manually at the moment of generating the cloze (or later).

This glossary entry is used to explain SuperMemo, a pioneer of spaced repetition software since 1987

Figure: Cloze interval in Algorithm SM-18 is not derived from the first forgetting curve. Using the optimum interval would result in inter-item interference. Instead, a random value of interval is chosen from the span determined by item's priority. Red line shows the lowest value of interval. The lowest value is 1 for high priority items, and around 12 for low priority items. The highest possible value of the cloze interval is shown in blue. It ranges from 1 to around 40. Cloze deletions with lowest priority (100%), will be scheduled in intervals randomly selected from the range: 12-40. Highest priority clozes will always use the interval of one day