Ring multisignature transactions can theoretically be implemented for any number of users and required signatures:
Suppose that a group of n users wants to create a multisignature address requiring t of the group to sign in order to spend any funds received, and in such a way that any observer will be unable to determine for certain whether funds have been sent from this address or not, but in such a way that spending funds twice is impossible
Although I am not aware of plans to facilitate placing specific time requirements for the completion of signatures for Ring multisig transactions, research has focused on some use cases where that feature would have value:
Another possible use of threshold multisignature is for an organization, such as the board of directors of a company holding company funds, or the developers of an open source software project holding donated funds, to control their funds in such a way that a certain number of members is required to execute any decision regarding the expenditure of those funds.
RingCT will provide multisig Monero transactions with unique anonymity related benefits not available in any other crytocurrency:
threshold signatures can be used in conjunction with the ring signatures, one-time keys, and ring confidential transactions of Monero to allow for anonymous threshold signature transactions with recipients, senders, and amounts obscured.