The topic is interesting, but I think the discussion of distances in space and speed of angels is mostly irrelevant in this context. First, the resurrection on the “third day” is no way exclusive to people in Urantia, but the same applies on all planets, on all locations. Second, they never say the three day -delay is due to travel or distance in space. Third, the “third day” -statement seem to apply also when there is no transition between places, like when Jesus arose from the tomb.
I cannot say how the resurrection on the “third day” happens, but the explanation must be somewhere else, than in traveling. E.g. are the Guardian Angels on Urantia, or do they “work remotely”. If they are on Urantia, so where do they stay if they look after a thousand people simultaneously?
The statement “third day” or “third period” is found dozens of times in The Urantia Book. Amazingly many things happen just on the third day, when somebody goes somewhere. Below I picked some of these.
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20:6.6 (229.5) When the bestowal Sons, Creator or Magisterial, enter the portals of death, they reappear on the third day.
35:2.8 (386.6) The Melchizedeks – – and then, following the correctional rest, reinstatement to service ensues on the third day.
62:7.1 (709.8) – – On the third day after the elopement of the twins – – there arrived the Nebadon archangel of initial planetary circuit establishment.
75:6.3 (844.5) The Edenic caravan was halted on the third day out from the Garden by the arrival of the seraphic transports from Jerusem.
93:10.1 (1024.3) – – And on the third day after his disappearance from Salem he [Melchizedek] appeared among his eleven fellows of the Urantia assignment
119:1.3 (1309.4) Not until the third day after Michael’s departure was any message of possible significance received. On this day a communication was registered on Salvington from the Melchizedek sphere, the headquarters of that order in Nebadon, which simply recorded this extraordinary and never-before-heard-of transaction: “At noon today there appeared on the receiving field of this world a strange Melchizedek Son – – [Ref. first bestowal of Michael]
119:2.7 (1312.1) And then did this transient ruler of a rebellious system take leave of the planet of his short administrative sojourn, while on the third day thereafter Michael appeared on Salvington and resumed the direction of the universe of Nebadon. – – [Ref. second bestowal of Michael]
119:3.4 (1312.5) – – the transitory or emergency Planetary Prince took formal leave, disappearing at noon one day. On the third day thereafter, Michael appeared in his accustomed place on Salvington – – [Ref. third bestowal of Michael]
119:4.2 (1313.5) On the third day after this bestowal disappearance we observed, in the universe broadcasts to Uversa – – [Ref. fourth bestowal of Michael]