When using the offline charts, the period separator seems to appear randomly. But in fact, it is not random. The period separator frequency depends on the offline chart ID you fill in the inputs. If you like to see the preferred separator, you should select the offline chart ID from its correct interval:

Value less than  H4 (240) results in a daily separator.

Value between H4 (240) and D1 (1440) results in weekly separators.

Value between D1 (1440) and W1(10080) results in monthly separators.

Value between W1 (10080) and MN1 (43200) results in yearly separators.

Values above MN1 are not supported by the MT4.