I can think of several ways to achieve this.  They all require you to be using 
RRDTool though.

First, you can load the data in using a script of your own, instead of MRTG.  
Keep a 'dummy' MRTG file around for the benefit of your web frontend, but dont 
run MRTG on it.  Instead, write your script to obtain the data, and then store 
it into the RRD file with an explicit timestamp, 45 mins in the past.  This 
will keep the data correct, and if you use the Routers2 frontend for MRTG/RRD 
you can set the 'uselastupdate' option in the routers2.conf so that the 
displayed graph will be based on the last update time rather than 'now'.

Second option is to write your own frontend or call to RRDTool to generate the 
graph.  An RRDtool function exists to shift data by a number of seconds 
time-wise so this would correct the offset; of course you'd need ot be using 
something like rrd-cgi to generate the graph and the command line would be 
pretty huge.

Third, you could define your own timezone of 'now-45min' and use that for the 
Target.  Since it would be displayed in the amended timezone this would effect 
a timeshift.  A bit messy, though, even if you can control the local server's 
timezone files (you cant do this on Windows as they're compiled into the 
library)

We have a similar problem for our mail server throughput logs, although the 
delay is only 10min.  We use the first method.

Steve

________________________________
From: [email protected] [[email protected]] On Behalf 
Of John Doe [[email protected]]
Sent: Saturday, 13 December 2008 10:20 a.m.
To: [email protected]
Subject: [mrtg] Applying a time offset to graphs

Hello,

I am relatively new to MRTG and I had a question that I did not see addressed 
in the documentation. I am monitoring a combination of Windows Server 
performance counters, which are updated immediately, and information retrieved 
from a database, which is not available until after a delay. As such, the 
"current" information being retrieved from the database sources is actually 45 
minutes old. What I would like to do is to shift the x-axis of the graphs of 
information from the database by 45 minutes so that if I am comparing one of 
those graphs to a performance counter graph, the actual times at which events 
are displayed match up.

Any help would be appreciated. Thanks!
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