As movies evolved, the standard running times – between 90 minutes and two hours – were gradually worked out according to the bums-on-seats scale.

That is, it was partly to do with estimating how long a regular paying customer might comfortably be expected to sit still, while still feeling they’d got their money’s worth, and partly – the larger part – to do with theatre owners calculating how many showings they could cram in per day.

Leaving aside the obvious factor, budget, how television producers work out how long it should take to tell a story is more mysterious, and, as we increasingly mould the way we consume TV to our personal desires, through box-set sessions or download catch-ups, grows hazier.

One of the most remarked-upon elements of the Danish thriller, The Killing, was that it was allowed to unfold over 20 episodes. Similarly, the deeper, denser stories in the best American imports – The Sopranos, The Wire, Mad Men – play across many, many hours. Then again, a single 70-minute Play For Today or 25-minute Twilight Zone could hit you hard and never leave you.

When it comes to adapting a book for television, you might imagine the issue would become more clear-cut: after all, the story is already laid out. In fact, the process seems completely arbitrary. We’ve had 10-hour Dickens adaptations, and we’ve just seen Michael Faber’s The Crimson Petal And The White as a solid four-part series.

So it’s hard not to feel Sarah Waters’s The Night Watch – a modern literary bestseller just as acclaimed and beloved as Faber’s – has pulled the short straw, getting rushed out in one underwhelming 90-minute lump.

The decision to treat Waters’s novel as a hasty one-off is more puzzling given the book itself suggests three clear parts. Following the intertwining lives, loves and losses of four characters in 1940s’ London, The Night Watch famously “runs backwards”, beginning in 1947, then moving back to 1944, then 1941, to reveal itself. As it is, this aspect is especially crassly handled: to signify time slips, images literally start rewinding, as if the makers felt they couldn’t trust viewers to understand the concept of a flashback.

The paucity of the adaptation is made starker considered against the HBO version of Mildred Pierce currently unfolding on Sky Atlantic. Physically (in page numbers), James M Cain’s book is far more slender, yet is granted a five-and-a-half-hour treatment that seeks faith to every paragraph.

Watching the condensed Night Watch, the sense is of a Wikipedia run through main plot points, with little of the stuff – blackout atmosphere, inner lives – that makes the novel.

Some fans of Waters’s book might get something, as they use their own memories to fill the gaps. However, viewers fresh to the story may wonder why they’re supposed to care, despite the best efforts of a cast led by Anna Maxwell Martin as the depressed Kay, whose brave central performance demands better, and even suggests what could have been.

It’s strange the BBC has chosen to make so little of The Night Watch when it has had such a productive relationship with Sarah Waters’s novels in the past. In 2002, Andrew Davies adapted her 1998 debut, Tipping The Velvet, as a three-part BBC serial that drew a lot of coverage as “the lesbian drama” and is worth treasuring for introducing wider audiences to Rachael Stirling. Davies was also behind the 2008 movie adaptation of Waters’s second novel, Affinity. Then, in 2005, the corporation also turned her Booker-nominated Victorian crime adventure, Fingersmith, into a fine three-part series, worth treasuring for introducing wider audiences to Sally Hawkins.