It takes from 5 (shortest) to almost 40 (longest) minutes for `bitcoin-cli gettxoutsetinfo` to return an _empty_ dict. I noticed this first whilst configuring the Statoshi branch of Bitcoin Core, but went back to install Bitcoin Core (git clone -b v0.11.2 https://github.com/bitcoin/bitcoin.git) to find the same results.

```
20:10 pi@raspinode:~/bin/bitcoin.orig $ bitcoin-cli gettxoutsetinfo
{
}
20:12 pi@raspinode:~/bin/bitcoin.orig $ bitcoin-cli getinfo
{
    "version" : 110200,
    "protocolversion" : 70002,
    "blocks" : 393193,
    "timeoffset" : 0,
    "connections" : 12,
    "proxy" : "",
    "difficulty" : 113354299801.47113037,
    "testnet" : false,
    "relayfee" : 0.00005000,
    "errors" : ""
}
20:17 pi@raspinode:~/bin/bitcoin.orig $
```

Raspberry Pi 2 - 1GB memory - 4 core CPU 900MHz - Blockchain on SanDisk Ultra Android microSDXC 128GB up to 80 MB/Sec Class 10

All other RPC calls through bitcoin-cli are answered promptly and correctly.
See also issue on jlopp/statoshi https://github.com/jlopp/statoshi/issues/19#issuecomment-171350739

#include "amount.h"
#include "chain.h"
#include "chainparams.h"
#include "checkpoints.h"
#include "coins.h"
#include "consensus/validation.h"
#include "main.h"
#include "policy/policy.h"
#include "primitives/transaction.h"
#include "rpc/server.h"
#include "streams.h"
#include "sync.h"
#include "txmempool.h"
#include "util.h"
#include "utilstrencodings.h"
#include "hash.h"
#include <stdint.h>
#include <univalue.h>
#include <boost/thread/thread.hpp> 
#include <mutex>
#include <condition_variable>
using namespace std;
struct CUpdatedBlock
{
    uint256 hash;
    int height;
};
static std::mutex cs_blockchange;
static std::condition_variable cond_blockchange;