Can the man's side pay the hantaran money in instalments or after the nikah?

Yes, if both families agree, because hantaran is a custom and not a pillar of the marriage. Unlike the mahr, which is obligatory, the hantaran does not affect the validity of the akad. So its form, amount and manner of payment can be freely negotiated. If instalments are agreed, write down the amount, the period and how it will be paid so nothing is forgotten. Allah says: “When ye deal with each other, in transactions involving future obligations in a fixed period of time, reduce them to writing” (Surah al-Baqarah 2:282). The man's side, for their part, should keep to that schedule because promises must be kept. To the woman's side: consider reducing the amount if instalments would burden your own daughter's new household. See the difference between mahr and hantaran.