I gave them notice to leave because I want to move back into apartment, as I want to move back into to as soon as possible I was happy for them to move out before the due date
If you have a fixed term agreement with the tenants, you cannot give them notice to leave just because you want to move back in. Basically, a fixed term lease cannot be broken by either landlord nor tenant except for breach of obligations.
Be very careful as there are very hefty fines for illegal eviction (10-20k). The tenants may appear to be willing to move, and then make a claim with the PRTB for damages for illegal eviction (especially tenants in the know).
If you did not sign an agreement with the tenants, then they probably have a Part 4 tenancy, in which case you can issue a Notice of Termination (in the prescribed manner as laid out in the Residential Tenancies Act 2004) on the grounds that you want the property for your own use. However, you must give the tenants the prescribed notice period, depending on how long they have been in occupation of the property.
If any Notice of Termination that you gave the tenants was not in written form and giving all the information required as per the RTA 2004, then the notice is invalid and you may be liable for illegal eviction.
To calculate the daily amount, take the monthly rent figure and multiply it by 12. Then divide the result by 365 and that gives the daily rent. Multiply the daily rent by the number of days to get how much they should pay.