Interesting article here on rte website.
Looks like some countries will potentially dig their heels in over an extension. It will need to have a purpose, rather than simply to allow more time.
Macron said. "The time has come for the British to make choices.We don’t need more time, what we really need is a decision… Under no circumstances would we accept an extension without a clear perspective [on the objective of an extension]."
A formal discussion at EU level on an extension is just getting under way.But behind the scenes the mood is darkening."Over the past six weeks member states, including those friendly to the UK, are being much more rigorous over the conditions under which an extension will be granted," says one senior source. "It can’t be just hoofing the ball around the long grass."
Another diplomat said: "The main condition is that there should be a purpose for this.It would be difficult if the extension is only there to prepare for no deal. The extension needs to lead to something: either an approval [of the deal], or a general election, or a referendum or whatever. A process that gives us clarity."
Also answers my own question re June
The preference would be for a short extension running up to the end of June, so that the European Parliament elections could go ahead without UK participation since the parliament does not have to be legally constituted until 2 July.