Probably a few weeks
Although there is nothing to directly reference to how long it took them to make a Super-Slave, we do get an idea at the start of the movie when we see Ajax delivering a bunch of Super-Slaves to the Warlord.
The Warlord asks about next months shipment and Ajax states that he is having a disruption to the supply chain. Now this on its own really does not say much because, lets say a disruption to supply for a 15 year old whisky would not affect anyone for another 15 years when that batch is to be sold. But Ajax says that he has to give his limited Super-Slaves to someone else, HOWEVER, will deliver in full the following month. So I am going to assume that it takes about a month to pump out a Super-slave.
So even though I can't say exactly how long Wade was in The Workshop himself, it was probably less than a month. Also, we are shown many of the torture methods and the longest seems to be the Oxygen tube, which seems to take a couple of days.
As to the time it takes for Wade to get into contact with his girlfriend, it was most likely about a little over a year from when Wade escaped from The Workshop to when he finally gets to talk to Vanessa.
In this scene:
I have been waiting one year, three weeks, six days and oh, 14 mins to make him fix what he did to me.
So based on that the story pretty much starts in real time from the highway fight scene and it is only a few days from when Ajax finally finds out that Wade is still alive to when he kidnaps Vanessa.
So it has been approximately one year and 3 weeks since he escaped The Workshop.