When casting a spell with a casting time greater than an action, do range and line of sight need to be maintained for the entire time?
For instance, does a cleric casting Prayer of Healing need the targets to be within 30 ft. and in line of sight for just the start of the spell, just the end or for the entire casting time.
Certain spells, such as Identify or Planar Binding, explicitly mention needing to stay within range for the casting time. Other spells like Magic Circle only imply you stay in range since the casting time represent drawing out the circle.
I'm fairly confident that one does indeed, need to stay in range at least. This line suggests that before a spell is cast, it remains limited by its range:
Once a spell is cast, its effects aren't limited by its range, unless the spell's description says otherwise.
I haven't found a rule requiring that one maintains line of sight.
The situation that this question arose from had an uncontrolled celestial being summoned into a magic circle. The wizard began to cast Planar Binding on it and realized that they could simply step into another room while they completed the spell, which seemed to trivialize what might otherwise be a very challenging task.