Calculate message transmission time

1) What is the best technique to calculate message transmission time? 2) Is it possible to calculate the transmission time using a 100 Mhz Oscilloscope, with the probe in the antenna connector? Or is it only possible to calculate the transmission time using a Spector Analyzer? 3) Which E220 settings directly impact message transmission time? Just the SpeedAirDataRate? 4) I need this information to try to identify the transmission time of a message sent by the E220, with the following characteristics: E220 - 920 Mhz Channel SpeedAirDataRate : 0 -> 9.6k (AIR_DATA_RATE_100_96) OptionSubPacketSett: 1 -> 32 bytes (SPS_032_11) Message Size: 15 bytes and Message Size: 20 bytes This information is important, as there are countries that only allow transmissions lasting up to 400 milliseconds.