The Champions Cup semi-finals will both take place on Saturday 26 September, the EPCR has confirmed.
Leinster will play at the Aviva Stadium at 1pm if they get through, regardless of opposition.
Ulster's fate is not as certain. They will be at home if it is against Northampton, but away if facing Exeter.
The second semi-final is schedule for 3.30pm.
Leinster face Saracens in a quarter-final this Saturday, while Ulster are in Toulouse.
Meanwhile the IRFU has confirmed that PCR testing of players and staff at Leinster and Ulster has produced zero positive results ahead of this weekend's Heineken Champions Cup quarter-finals.
A total of 191 players and staff have been tested across the two provinces this week.
Heineken Champions Cup semi-finals:
Saturday 26 September
- SF 1: Winner Leinster/Saracens v ASM Clermont Auvergne/Racing 92 at 1pm.
- SF 2: Winner Exeter Chiefs/Northampton Saints v Toulouse/Ulster at 3.30pm.
Follow the Champions Cup quarter-final between Leinster and Saracens (3pm Saturday) with our live blog on RTÉ Sport Online and the RTÉ News app or listen to live commentary on RTÉ Radio 1