The UK Takeover Panel has given Ion Investment Group and SS&C Technologies 10 days to put in a firm offer for Fidessa.
Fidessa reached an agreement with Swiss banking software firm Temenos in late February for a $1.4bn cash sale which was due to be signed off by shareholders last week.
However, the vote was postponed until 27 April when Fidessa revealed that two firms - Ion and SS&C - had made approaches and were considering offers at a premium to the Temenos deal.
Now, the Takeover Panel has given Ion and SS&C until 5pm on 20 April to either announce a "firm intention" to make an offer or bow out.
Meanwhile, Temenos says that it has received unconditional approval from the FCA for a takeover and has also received notice of the early termination of the waiting period for US antitrust review.