Can I treat money not saved before retirement as spending?

Yes. To model this approach, enter the amounts you intend to save under AUTOMATIC SAVINGS and WITHDRAWALS. Then put Spending first in deposit PRIORITIES with a 100% limit for the relevant years and household members. The surplus remaining after entered costs, taxes and automatic savings will be spent rather than deposited to another account. TIME MACHINE reports it as Unspecified Spending.

For retirement, enter the annual after-tax living costs you want under EXPENSES, starting at retirement. An expense can be Joint when both spouses share it. Set priorities for the retirement years according to how you want any remaining surplus handled; priorities from earlier years can otherwise continue to apply.

You can omit a detailed pre-retirement living-cost budget with this approach, but still enter expenses needed for their specific treatment: tax-deductible or tax-credit expenses, education expenses linked to RESPs, and medical expenses paid from a U.S. Health Savings Account.

CHOOSE YOUR LEGACY is another way to calculate spending for a chosen after-tax legacy. To use that tool, set the Spending deposit-priority limits to 0%; otherwise the priority can spend the surplus that the tool is trying to allocate through expense adjustments.