A suggestion to compute time estimates for different time settings and board sizes:
numberOfMovesPerPlayer = round(boardWidth * boardHeight / 3)
Fisher: totalTimePerPlayer = intitialTime + min(fisherMaxTime, numberOfMovesPerPlayer * increment)
Simple: totalTimePerPlayer = numberOfMovesPerPlayer * timePerMove * 0.75
Byoyomi: totalTimePerPlayer = mainTime + (numberOfMovesPerPlayer + periods - 1) * byoyomi * 0.75
Canadian: totalTimePerPlayer = mainTime + (numberOfMovesPerPlayer / stonesPerPeriod) * overtimePeriod * 0.75
Absolute: totalTimePerPlayer = totalTime
(time units of all parameters are the same)
And the timePerMove = totalTimePerPlayer / numberOfMovesPerPlayer
Then maybe the game should be unranked/signaled when timePerMove is less than 4s or more than 60s for live/blitz. And maybe the boundary between live and blitz is at about 10s timePerMove?
You can play (and maybe find bugs) with this google spreadsheet. Edit the bold numbers (note the units, m = minutes, s = seconds) to see numbers change in the F and G columns.