Slattery only failed to make the squad once - on 26th December against Livi when he was suspended.
He started 28 games, was subbed on in 6 and was an unused sub in 8. So from the point he signed he was in the match day squad for 42 of 43 games.
He played the 6th most minutes of the squad behind Kelly, O'Donnell, Mugabi, Van Veen and Woolery.
Source: https://www.transfermarkt.co.uk/callum-slattery/leistungsdaten/spieler/332342