There is no objection in paying for Hajj through installments. It is, however, best that you do so when you can pay for the entire Hajj in one installment. Hajj, as we should know, is obligatory only on those who can afford it financially and physically.

However, since Islam is a religion of ease and mercy, one may pay for it in installments as long as one is solvent and can pay off the debts, in the case of any unforeseen circumstances of death or incapacitating illness.

Allah Almighty knows best.