Alpha strike is roughly 30 seconds to 1 minute, from a stats on a card POV. The OG stats were based off of a 30 second battleforce turn, but when converting to alpha strike you can do more in 1 alpha strike turn then in 3 battletech turns (like, damage rounds up, meaning more then 1 battletech shots of a medium laser are being taken to deliver the 1 alpha strike damage/30 classic armor damage, so 3 to 6 turns of classic are happening to do the listed alpha strike damage).
As for model scale, the game (like many) has a scale issue where it trys to make height on the table be 'mech scale ish' so that 2 inches of vertical terrain blocks LOS to mechs. This leads to very tiny battlefields due to the game trying to kinda match scale to minis. By game stats this cant be reconciled, as a 5 hex mech can move 10 inches, for ~75m, leading to 'long range' at 42 being only 315 meters, and 5 second turn times (instead of 30-60 second turn times). So alpha strike map scale and gameplay scale disagree by a factor of 6-12x, a consequence of wanting to use true LOS terrain for the models. 40k has the same problem with very short/small ranges as a result of using minis with true LOS terrain.