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

{
    return "    \"size\" : n,             (numeric) transaction size in bytes\n"
           "    \"fee\" : n,              (numeric) transaction fee in " + CURRENCY_UNIT + "\n"
           "    \"modifiedfee\" : n,      (numeric) transaction fee with fee deltas used for mining priority\n"
           "    \"time\" : n,             (numeric) local time transaction entered pool in seconds since 1 Jan 1970 GMT\n"
           "    \"height\" : n,           (numeric) block height when transaction entered pool\n"
           "    \"startingpriority\" : n, (numeric) priority when transaction entered pool\n"
           "    \"currentpriority\" : n,  (numeric) transaction priority now\n"
           "    \"descendantcount\" : n,  (numeric) number of in-mempool descendant transactions (including this one)\n"
           "    \"descendantsize\" : n,   (numeric) size of in-mempool descendants (including this one)\n"
           "    \"descendantfees\" : n,   (numeric) modified fees (see above) of in-mempool descendants (including this one)\n"
           "    \"ancestorcount\" : n,    (numeric) number of in-mempool ancestor transactions (including this one)\n"
           "    \"ancestorsize\" : n,     (numeric) size of in-mempool ancestors (including this one)\n"
           "    \"ancestorfees\" : n,     (numeric) modified fees (see above) of in-mempool ancestors (including this one)\n"
           "    \"depends\" : [           (array) unconfirmed transactions used as inputs for this transaction\n"
           "        \"transactionid\",    (string) parent transaction id\n"
           "       ... ]\n";
}
void entryToJSON(UniValue &info, const CTxMemPoolEntry &e)