Draft Law 4020 has been adopted by the Ukrainian government. The law, instigated by President Poroshenko, allows the President, in 'special circumstances' e.g. during military mobilisation, to give only one months' notice of the draft. Notice is given in the media.
However, conscientious objectors who wish to apply for an alternative service need to apply two months before their call up. So in theory, if this practice is applied, it may make it impossible to take advantage of the right of alternative service.
Source: Human Rights Without Frontiers, Rights of conscientious objectors in Ukraine threatened, 18 February 2016; Institute of Religious Liberty, Принят законопроект Президента, усложняющий альтернативную службу, 18 February 2016