This was a Lucy Powell amendment to Hillary Benn’s amendment – which, itself broadly speaking, seeks to give control of the Brexit negotiation to the Commons after an extension.
Powell’s suggested an extension cut-off date of June 30. This was presumably aimed at getting the Commons to make a decision by that date – after which the present default of No Deal would kick in.
She is what this site calls a Norwegian – i.e: a backer of Norway Plus / Common Market 2.0. So the aim of her amendment was to set conditions under which the Commons would be likely to back this Soft Brexit scheme.
The logic of the ploy was to establish a timeframe too short for an effective Second Referendum push. If May’s deal was dead, Norway Plus would therefore be left as the only alternative on the table.