Should I invest into SSB in one lump sum or separate them into different months?

If you got the DBS multiplier account buy for 6 months to build a bond ladder

if not a one time lump sum will help reduce the total cost of investment

another consideration is the raising rates of interest so it might make sense to take a more cautious approach

One lump sum.

1. Each application cost $2 (to buy or redeem early).

2. All your money goes into work to earn returns immediately. Money sitting at the sidelines are not working.