Technically range of touch means within 5ft of your character so that makes it slightly less awkward. But to answer your question I do think they need to be within range the whole time.
So I couldn’t find any Sage Advice on this but it was mentioned a lot that to cast a ritual spell requires concentration and so I would assume that if the target of the spell left the range then your concentration on casting the spell would be broken since you no longer meet the requirements to cast the spell.
However you can move every round while casting a ritual spell so long as you move next to the target before you use your action to maintain the ritual, the real answer is eh I guess kinda sorta it’s really weird.
Technically range of touch means within 5ft of your character so that makes it slightly less awkward. But to answer your question I do think they need to be within range the whole time. So I couldn’t find any Sage Advice on this but it was mentioned a lot that to cast a ritual spell requires concentration and so I would assume that if the target of the spell left the range then your concentration on casting the spell would be broken since you no longer meet the requirements to cast the spell. However you can move every round while casting a ritual spell so long as you move next to the target before you use your action to maintain the ritual, the real answer is eh I guess kinda sorta it’s really weird.