'Then' can mean a particular time in the past or in the future. Translate with 'allora' for the past and 'poi' or 'dopo' for the future.
'Ritardo' is a noun not an adverb (cognate with 'retard') : Un ritardo di una ore - an hour delay'. To make it more complicated: 'In ritardo' is an adverb: 'Essere in ritardo - to be late.
You can get a sense if it is used often by seeing it in context using Reverso Context: http://context.reverso.net/translation/italian-english/prima+o+poi It seems to be used fairly commonly, but a native Italian speaker will have to verify.