The phrase "an additional three days" is correct and usable in written English.
You can use it when referring to an extra period of time added to an existing timeframe or deadline.
Example: "Due to unforeseen circumstances, we will need an additional three days to complete the project."
Alternatives: "three more days" or "an extra three days".
The cells were then pretreated with 1.0 µM CGS21680 for 30 min followed by the addition of 1.0 µM ZM241385 or exposure to SMF for an additional three days followed by staining with F-actin conjugated with Oregon Green488 phalloidin (1∶100) (Molecular Probes, now Invitrogen, Eugene, OR).
The maximum stock we can put in the pipeline is an additional three days for which we have had to make additional investment.
Before the firing, an additional three days is required to load the apparatus, which vaguely resembles a dragon, with roughly 1,200 clay pieces.
He was speaking on Tuesday before it was announced that the Vienna negotiations between Iran, the US and five other world powers had been extended for an additional three days after missing a second deadline.
The Archdiocese of Washington predicts that the pope's three days in the capital, starting on Tuesday, will cost at least $3 million, but the Archdiocese of New York, where he will spend an additional three days, has not ventured an estimate.
It begins on the 10th of Dhu'l-Hijja, the last month of the Islamic calendar, and continues for an additional three days (though the Muslim use of a lunar calendar means that it may occur during any season of the year).
Patients treated with MIC who tested positive for Candida albicans (CA) were switched to FLU and received an additional seven days of treatment for a complete 10-day course, while those treated with FLU empirically and testing positive for CG or CK were switched to MIC for an additional 10-day course of appropriate coverage.
Following the addition of cytokines, cultures were incubated for an additional eight days.
The fresh weight (FW), leaf area, dry weight (DW), CO2 assimilation rates (CA), dark respiration rates (DR), and transpiration rates from 26 day-old radish plants that were grown for an additional seven days at different total pressures (33, 66 or 101 kPa) and pCO2 (40 Pa ,100 Pa and 180 Pa) were measured.
The rats were passively trained for an additional two days as described above with one striped wall, before on the third day receiving a probe (Test trial) that now used two black and white striped walls arranged next to each other for the first time.
The court granted him an additional eight days to appear.
