Timing on any motor is more dependent on when the Hall Effect sensor sees the rotor. This depends on the sensor to a limited extent, but more on the clearance between the sensor and the rotor. So, any attempt to say accurately what the timing is on a motor is doomed to failure. All motors come with timing, even when they say 'zero'. Take a look inside the can and see where the sensors are when the marks/inserts say zero - they're hardly anywhere near TDC, or zero!
Let's accept for a moment that wherever the sensor physically is, you have 0 degrees timing. As the motor has three coils, they are spaced 120 degrees apart from centre-of-(magnetic)-field to centre-of-field. Therefore, is you increase the 'timing' beyond 60 degrees, you put the timing point on the edge of one field. There's a chance that the rotor won't clear one 'field' before it sees the next one, and it may stall. So, as a rule-of-thumb, any timing setting beyond 60 degrees is not advisable as you cannot know the motor load when it reaches 60 degrees, and so you risk slowing the motor down and generating excess heat.
As to the practicalities, because you cannot know accurately where the sensor sees the rotor, or where 'zero' is, it is highly likely that some motors will run OK with what appears to be 70 degrees total - 60 degrees is only a rule of thumb after all! - but some won't, and may object by ceasing to function and demanding more $$$ from your credit card!
The problem you all have now is that there are no rules to follow when gearing and timing BL motors. Not only is every motor different, motors with the same model number can behave slightly differently when you get to extremes of timing. Anyone asking "what ratio do I put a 13.5 on?" might just as well ask "how long is a piece of string?" - it depends where you cut it!
The ONLY way to get the best from your motor is to experiment with it. Base settings are fine, and can be copied, but you need to start 15% lower on ratio to see how it goes. Only then can you gradually get up to the ratio you were given, and then try different profiles to see of there's any more speed left to get. The thing to remember is this - a DC electric motor 'retards' as the load build up. That means that if you throw too much timing at it too early, it will just get hot and slow down. The more it can rev, the more timing you can throw at it. So, ratio, motor timing, speedo timing and track requirements must all be factored in, and balanced to get the best lap time.
Sorry that you don't have a single answer to work with. There's an old saying - "If you can keep your head while all around are losing theirs, you don't understand the problem!" (With apologies to Rudyard Kipling) Anyone who tells you there is a simple answer doesn't understand the problem!!
My advice is to stick to less than 60 degrees, try any set-up you like but take 15% off the gear ratio to start with, and most of all never let a single race go by where you don't try something different. Write each race settings down, put a lap time next to it, and learn. HTH