Retirement tax questions

In my case, employer pension is fixed, except for the ocassional minor inflation adjustments.  What makes my 2024 income different from 2023's is rental income/expenses due to a vacancy + above average repairs with legal expenses. 

Because I'd like to Roth-convert portions of my Traditional Rollover IRA over the next 10+ years, the moving target (rental income/expenses) will make it difficult for me estimating how much I should convert each year. For 2024, for example, the Standard Deduction changed from 2023's, the tax tables are not the same as 2023's, etc.  In summary, rental income/expenses make my income tax returns different every year. This is why I think I need to know what my tax return will look like w/o a Roth conversion, so I can then (by iteration) decide what amount to Roth-convert.

I am currently doing a mock-up income tax return using Turbo Tax for 2023 and entering my values for 2024, and I am not sure this is even a good use of my time.....

If the IRS allows a working citizen to make pre-tax IRA contributions for 2023 as late as 4/15/25, why couldn't we also do Roth conversions for 2024 as late as 4/15/24?  I understand, this is not allowed, so why can't the tax software be ready for use before at the very least a week before the tax year ends?