Beamup, as I understand it, it is legal to gift a city - it is also legal for Dantski to accept this city - everything happening in the same turn.
What is not legal is to interleave there moves. Basically if Dantski goes first, his part of the turn timer ends as soon as Spullla starts to move units. He is allowed to change city builds then, slave and change worked tiles but thats it. He is not allowed to do anything which changes the war. And accepting the gifted city certainly does change the war.
edit: It gets easy if you think about it as if all 3 parties involved in this war do have 8 hours each for making their moves which affect the war.
What is not legal is to interleave there moves. Basically if Dantski goes first, his part of the turn timer ends as soon as Spullla starts to move units. He is allowed to change city builds then, slave and change worked tiles but thats it. He is not allowed to do anything which changes the war. And accepting the gifted city certainly does change the war.
edit: It gets easy if you think about it as if all 3 parties involved in this war do have 8 hours each for making their moves which affect the war.