I have done a lot of reading on this subject and to be honest I do not believe changing salinity by a large value at once is the smart thing to do and IMO a .003 raise in one shot is a large increase in my book. Your specific gravity is 1.020 as you mentioned which is 26.6ppt ( PSU ). A .003 increase in one shot will raise it to 30.6ppt. If you don't have any corals you may be safe but from all I have read the max daily change in salinity for fish only should not exceeded 2ppt. If you have corals, especially SPS, from what I have read the change should be far less than 2ppt to be safe. IMO if you want to go from 26.6ppt ( 1.020sg ) to 35.1ppt ( 1.0264 ), for fish only I would only increase 2ppt per day for 4.25 days. If you have corals, and if it was me I would only change the salinity by 1ppt per day for 8.5 days. Remember during the time you are changing the salinity to get to your goal you will have evaporation and unless you have an ATO you may need to adjust the values slightly so checking salinity daily is recommended IMO.
Again this is what I would do to be safe. Slow is better than too fast with almost anything with a reef tank.