@Poli: The subjunctive is triggered by the verb "desear", so your proposal: "si no lo hago hoy, mañana lo lamentaré/tendré remordimiento(s)" is correct, as both verbs correspond to the moment:
- "hago" (present -> "today")
- "lamentaré"/"tendré" (future -> "tomorrow")
You might hear "mañana lo lamento", but this is very colloquial speech. Not recommended.
@Bobbert: Glad to help.
