Jane Tanner wasn't at the table when the alarm was raised.
The others reacted in exactly the way I would expect them to on hearing such shocking news - and seeing the state of distress KM was in. It would be unnatural for them not to IMO.
Not according to these two timelines written by her partner that night after the alarm was raised:
http://www.mccannfiles.com/id261.html#tap19
Those timings were written down a couple of hours after Madeleine disappeared. They were at best 'hurried' estimates - and cannot be regarded as accurate or containing all the detailed info at such a stressful time. I didn't see anywhere that Jane Tanner was placed at the table when KM gave the alarm.
JT had returned to the table (after seeing 'the abductor',) then went back to the apartment again later (9.45ish) to relieve Russell. The restaurant staff cooked a fresh meal for him because he had been away looking after Evie and his meal had got cold. He returned to eat it and JT stayed with their daughter who was unwell. She was still there when the alarm was raised.
None of the times given (apart from Gerry's who looked at his watch at 9.05) - can be regarded as completely accurate. It would only be by going over the evening together that their combined recollections could eventually arrive at what were the most accurate times, and most accurate sequence of events, as what one person had forgotten, another might remember etc - but even then they would still only be approximations.
IIRC, one of the group originally thought that JT and Gerry had left the table together - (when GM met Jez). However during later discussion no doubt Jane (or others) would point out that she was still at the table when they began making jokes about why Gerry had been gone so long (watching the footie) - so then that person would accept that he/she was mistaken. I see nothing to criticise in their discussing times etc as none of them had any reason to remember precise times until AFTER Madeleine disappeared. It was only then that it became so important.
All IMHO.