Probably quite a while, the DUP have backed nearly every decision that the Conservatives have made over the last few years anyway, particularly as concerns austerity. They are also fully behind a hard brexit thanks to some tactical large party donations, and are even more corrupt (look up the DUP's renewable heating incentive scandal to see what I mean.) They're a match made in hell.
Where it may fall down is if the DUP demand a return to direct rule for Northern Ireland. Since the assembly election a few months ago Sinn Fein are only one seat behind DUP as the largest party, and they no longer have then numbers required to veto legislation on gay marriage etc. So since the election they've been intentionally dragging their feet and sabotaging the negotiations intended to get the assembly back to work, in the hope that devolution will end and we will be returned to direct rule from Whitehall.
The only thing is, under direct rule the courts would eventually have to rule that women in NI must have the same access to abortion as in England and Wales, gay marriage would available here etc. Not at all what the DUP want to happen.
So the way I see it the DUP's support will probably be stringent on having the Tories allowing them to continue keeping Northern Ireland as their own personal fiefdom separate from the law of the land in the UK, yet suspending the assembly so as to not allow Sinn Fein and the other parties to democratically overrule them.
This exposes the biggest irony of modern unionism: the claim of loyalty to Britain and soon it seems to be part of their government, but also the desire to be exempt from those pesky modern British laws like equal rights. So while the DUP are going into this probably thinking that they can coax the Tories into rolling back on gay marriage and restricting abortion etc. the opposite will probably be true. The weight of public opinion against the DUP's backwardness will hopefully force Northern Ireland into line legally with the rest of the UK, into the 20th century.
Interesting times ahead anyway.
Sept 7|B'fast|Rose Tattoo+Girlschool
Sept 27|B'fast|RBOTN+Midnight Force
Oct 10|B'fast|Enslaved+High On Fire