We know that the IRS is already revising the 2020 Form 1040 to include the 2nd stimulus, but that change will entail a lot of re-programing at the IRS and for the tax software programs. It may be at least a month — or longer— before the forms are changed. Do NOT be in a hurry to file your 2020 tax return until more is known. Give some extra time to the IRS and the software programmers so that the software can handle the new 2nd stimulus, so that you can get it all by filing ONE time. It is never a good idea to file too early; filing your 2020 return too soon may result in a lot of extra confusion that can be avoided if you wait and file a little later.
NO ... the form is not yet ready for filing yet so just wait for the programming to be completed. And the IRS will not start processing returns until the end of January so there it no need to rush. And if you are using the downloaded version any overrides in the forms mode will keep you from efiling when that option is available AND voids the accuracy guarantee ... so there is no upside to this thought.
And you do not enter the amount you have coming directly on line 30 ... it is used on the line 30 worksheet.
ALSO, the form that calculates Line 30 is quite complicated as it takes your 2020 income, filing status and dependents under the age of 17 and compares to the payments you received to date.
It is not as straight forward as one would think!
What is that warning you see on TV? "do not try thing at home yourself!"