Unfortunately though a phone call to the court is an utterly absurd suggestion. Why would you assume anyone answering the phone would even know?
Like all other rules of court, you have to look it up yourself, and stand or fall by that. I've had a quick look myself and the ECHR own site links to the relevant materials and these make it clear that an appeal must be delivered to the Court within 3 months
including the day of the judgment appealed against. Doesn't seem therefore to be any room, at all, for doubt.
The Court's own general rules contain the same calculation. It's easy. Either the day of the judgment counts as day 1, or it does not, and in this case it indisputably does.
As I suspected, May can, it seems, count.