если дословно - "быть длинным в следовании"

The prevailing pattern here is TO BE LONG IN -ING which basically means that something didn't happen right away: His first movie was a hit, so it was surprising that the sequel was so long in following. (=took so long to follow the first movie). In the negative, it expresses expediency: On his first day at work, the boss gave him a rather difficult order and Andrey was not long in following. (=he followed the order right away). Note that this is not a conversational construction - it's mostly used in descriptive writing.

... было удивительно, что продолжения пришлось ждать так долго.
... Андрея не пришлось просить дважды.

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