The Hitchhiker's Guide to the Galaxy would have this to say about the Labour Party's attitude to by elections in their gift, had the editor on Alpha Centurii ever got around to amending the entry on Earth from 'Mostly Harmless' to something with a little more flesh.
The approach that Labour have to on of their members dying is confusing, no confusing that that. Think of the difficulties the male of the various species have had in pleasuring Eccentrica Gallumbits the triple breasted whore of Eroticon Six. Then, as rumour has it, the only person to give her the biggest bang since the big one had a extra arm fitted or the purpose. Of course the fact that said arm belonged to one time President of the Galaxy, and fugitive space joy Zaphod Bebblebrox and you might just get to the level of confusion required.
The Labour Party in the United Kingdom (a rather small sea locked mixture of islands at what was once erroneously considered to the be the North West corner of the world) actually change their mind on what is appropriate when one of their Members of Parliament dies or for that matter resigns.
There have been occasions when they rushed out a tribute leaflet within days of the funeral, and moved a writ to replace the deceased before the worms have even managed to get a sniff of the delights within the wooden casket, let alone been able to move into the vicinity of the meat counter. It is clear that on these occasions it is highly appropriate to have had discussions in private about the timing and actions to be taken. Indeed it is apparent that in the past their thoughts haven't always been "completely with" the family of the deceased.
However, there are times as the ape descended carbon based lifeform Mark Reckon's points out when they seem to want to hold off. However, as was later unearthed at the time of the second coming of the Great Green Arklesiezure this was because they did not heed the far larger death to come of the New Labour project itself.
As Mark points out with the exception of Glasgow North East 42 working days would be above average for the period from writ to by election. If Labour hold off beyond that expect a March election to negate the need to move the writ.